An early look at the 2012 landscape shows Democratic incumbents are the most vulnerable heading into the next cycle, with double the number of Democrats on the ballot as Republicans.

Senate Democrats have no obvious pick to lead the Democratic Senatorial Campaign Committee, and they face an enthusiastic and newly buoyed Republican caucus with a real chance at winning back control of the chamber in two years.

There are 33 seats on the ballot on Nov. 6, 2012. The field will narrow and grow complicated as Senators inevitably decide to retire along the way and as contenders step up to run. But here’s a comprehensive look at the map as it stands today. Roll Call Politics has seven states in the Tossup category and 12 states that are only in the Leans category to remain held by the respective Senator’s current party. Several Republicans may face primaries from the right, but GOP operatives tell Roll Call their bosses learned their lessons from watching Sen. Bob Bennett (Utah) lose the Republican nomination at a convention and won’t take their party’s support for granted.

Here are the Roll Call Politics race ratings as they stand today — before most challengers are known and as not a single Senator has announced his or her retirement.

Tossup

Connecticut

Sen. Joe Lieberman (ID)

This race should be among the more entertaining this cycle, although much will depend on Lieberman.

The four-term incumbent has yet to decide if he’ll run again. And if he does, it’s unclear whether he’ll run as a Democrat or Republican or keep his current Independent label.

There isn’t an easy path. He will almost certainly face a competitive primary should he run with either party, and there is broad agreement that a second Independent run could spell disaster given his low approval rating back home.

That’s because Republicans ran only token opposition in 2006, allowing Lieberman to claim victory with substantial GOP support. That’s far less likely this time around, as a possible field of far more credible challengers has already emerged. People to watch include unsuccessful 2010 Senate candidate Linda McMahon, businessman Christopher Meek, former Rep. Rob Simmons and 2010 gubernatorial nominee Tom Foley.

On the Democratic side, possible contenders include Rep. Christopher Murphy and Edward Kennedy Jr., son of the late Senator and an investment banker.

Lieberman, of course, could always choose to retire, although he reported $1.3 million in his war chest as of Sept. 30.

Florida

Sen. Bill Nelson (D)

Nelson, first elected in 2000, intends to seek a third term. His campaign team sounds confident he will win over the state’s voters despite Republican gains in 2010 statewide, and he has $2.9 million in the bank. Nelson easily deflected former Rep. Katherine Harris in 2006.

Florida, always a critical battleground in a presidential year, will hold even more importance for White House contenders in 2012, so expect money and attention to flow to the Sunshine State sooner rather than later.

Florida Republicans say they have an abundance of potential candidates to challenge Nelson, though no one has stepped forward with an official announcement.

“Republicans here are really eager to take out the last remaining statewide Democrat,” said Republican Party of Florida spokesman Dan Conston.

Republican Sen. George LeMieux, appointed by Gov. Charlie Crist to fill the remainder of Sen. Mel Martinez’s term when the Republican resigned from the Senate, would be a strong favorite should he decide to run. LeMieux has been open about his interest in challenging Nelson, telling reporters he will decide over the holidays, but his office did not respond to calls seeking comment.

After LeMieux, Republicans like the incoming state Senate president, Mike Haridopolos. A GOP source said he is considered among the party’s up-and-comers.

Republican Reps. Connie Mack IV, Vern Buchanan and Tom Rooney also are on the bench. Buchanan and Rooney could be self-funders should they run, making them more appealing to the state party.

State House Majority Leader Adam Hasner is term-limited from that position and is another possible contender, and a perennial dark horse is former Gov. Jeb Bush.

Massachusetts

Sen. Scott Brown (R)

Regardless of his opponent, his current popularity or the size of his bank account, Brown is in serious danger of losing his place in the Senate.

Despite his shocking January 2010 victory in the special election to fill the seat of the late Sen. Edward Kennedy (D), Massachusetts remains a deep blue state. Lest there be some doubt, Bay State Democrats captured every statewide office and Congressional seat earlier in the month, beating back the conservative movement that shaped elections in other Democratic-leaning states across the country.

If Brown were serving in another state, he might be a shoo-in for re-election, though he has irked some in the tea party movement for voting with Democrats on financial reform and a jobs bill.

Brown reported nearly $6.8 million in his campaign account at the end of September. Public polling released in mid-October showed better approval ratings than President Barack Obama and senior Sen. John Kerry (D).

Democrats have yet to find a challenger, but any Democrat with moderate name recognition will become an instant threat.

People to watch include Reps. Mike Capuano, Stephen Lynch and former Rep. Marty Meehan. City Year founder Alan Khazei has also been a rumored candidate, as has Boston Mayor Tom Menino.

Missouri

Sen. Claire McCaskill (D)

McCaskill has to watch her back after Republican Rep. Roy Blunt defeated Democratic Secretary of State Robin Carnahan in this year’s Senate race. Both parties agree the state will be a central battleground. McCaskill was narrowly elected to unseat Sen. Jim Talent in 2006, and a rematch in the longtime battleground state is a strong possibility in 2012.

If Talent forgoes the Senate race, a number of other Republicans will have to make a choice between running against McCaskill or Gov. Jay Nixon. Ann Wagner told the KMOX radio station in St. Louis she is “seriously considering” a statewide run. Wagner was chairwoman of Blunt’s Senate campaign after serving as ambassador to Luxembourg and as co-chairman of the Republican National Committee. Lt. Gov. Peter Kinder, a former state Senator and aide to the late Rep. Bill Emerson (R), has also been mentioned as a potential statewide candidate, as has Sarah Steelman, the former state treasurer and state Senator who lost a bid for governor in 2008.

McCaskill had $614,000 in the bank as of Sept. 30. The presidential race will be a factor in the state in 2012; Democrats have long attempted to put Missouri within reach, and President Barack Obama’s team came close in 2008. Obama lost Missouri to Sen. John McCain (R-Ariz.) by fewer than 4,000 votes out of 2.9 million cast. That result marked only the second time since 1904 that the Show-Me State did not vote with the White House victor.

The Democratic National Committee is considering St. Louis for the location of the 2012 national convention, a move they hope will tilt the state in their favor.

Nebraska

Sen. Ben Nelson (D)

After promising that he will run for re-election as a Democrat, Nelson, a moderate who is the only Democrat in Nebraska’s Congressional delegation, established himself as one of Republicans’ top targets in 2012.

The Nebraska Republican Party took a poll on Election Day and the following day that showed only 36 percent of Nebraskans thought Nelson deserved re-election, and 55 percent said it was time for someone new.

Nelson had $1.4 million in his campaign account at the end of September, and in December 2009 ran his first 2012 campaign ad to explain his position on health care.

Nelson got a break when popular Gov. Dave Heineman (R) declined to run against him, but Attorney General Jon Bruning got in immediately after Heineman’s announcement. Bruning explored a run for the Senate in 2007 when Sen. Chuck Hagel (R) began looking into a presidential run, but when Hagel retired, Bruning deferred to former Nebraska Gov. Mike Johanns, who ultimately won the seat.

Don Stenberg, who was elected state treasurer on Nov. 2, has also said he may run against Nelson. Nelson defeated Stenberg, a former attorney general, in the 2000 general election. Stenberg also lost Senate primaries in 2006 and 1996. State Auditor Mike Foley hasn’t ruled out a run.

Nevada

Sen. John Ensign (R)

Speculation had been rampant over whether Ensign would run for re-election, but the scandal-plagued Republican told reporters this week he plans to seek a third term. Ensign, under federal investigation regarding an affair he had with a former staffer, has blown through much of his campaign cash to help pay for his legal fees and had just $280,000 in the bank and owed more than $20,000 as of Sept. 30.

The top Republican waiting in the wings is Rep. Dean Heller, who won a third term on Nov. 2 and would be considered a formidable statewide candidate. The Las Vegas Sun’s Jon Ralston wrote recently that Ensign would be “flattened” by Heller in a primary, though a poll taken in October by the Democratic firm Public Policy Polling showed Ensign beating potential GOP rivals.

Other possibilities include former Rep. Jon Porter, Lt. Gov. Brian Krolicki and Sharron Angle, who just completed an expensive and unsuccessful challenge for Senate Majority Leader Harry Reid’s seat.

Democrats mentioned so far include Rep. Shelley Berkley and Secretary of State Ross Miller.

West Virginia

Sen. Joe Manchin (D)

Republicans are treating Manchin like he is their prime target in 2012, going after the former governor of West Virginia as if he had already announced he was seeking re-election. Manchin won a special election to serve out the remainder of the term of the late Sen. Robert Byrd (D) and would face voters again in two years.

His office, preparing for the transition since Manchin was sworn in Monday, did not respond to repeated calls for comment about his political future.

West Virginia Republican sources said Rep. Shelley Moore Capito (R) is the “obvious” choice to run for Senate in 2012. Should she pass on a bid, former Secretary of State Betty Ireland would be the best candidate, the sources said. Beyond that, there is a relatively thin bench with any statewide name recognition, a situation the GOP sources said spells chaos for the party two years from now if Capito does not run.

If Manchin does not seek re-election, one potential candidate is former Sen. Carte Goodwin, whom Manchin appointed to the seat after Byrd’s death this summer. But Goodwin may choose to run for state office or Congress instead, depending on the results of redistricting. Another name mentioned on the Democratic side is state Supreme Court Justice Robin Davis, who would be able to self-fund her candidacy.

Manchin’s election leaves the governor’s mansion vacant, so the race to replace him will be the next contest commanding Mountain State voters’ attention. Sources from both parties think candidates to challenge Manchin will emerge once that race shakes out.

Leans Democratic

Michigan

Sen. Debbie Stabenow (D)

Stabenow is planning to run for re-election, but it’s unclear whom her opposition will be. She was re-elected in 2006 with 57 percent of the vote over a county sheriff. In 2010, Republicans made gains everywhere in Michigan, picking up the governorship and two House seats, as well as retaining control in the state Senate and winning control in the state House.

Since Michigan is likely to lose a House seat in redistricting, any of the state’s nine Republican Congressmen might have reason to consider challenging Stabenow. She has a $1.6 million campaign war chest.

Minnesota

Sen. Amy Klobuchar (D)

Minnesotans are still focused on 2010’s undecided gubernatorial race, but that’s no reason for Klobuchar to get comfortable. Elected over Republican then-Rep. Mark Kennedy in the open 2006 race, Klobuchar represents a state that in 2010 ousted longtime Rep. Jim Oberstar (D) in favor of little-known Republican Chip Cravaack and that has been known for its independent streak. Klobuchar had $1.3 million in the bank as of Sept. 30.

A number of Republicans are beginning to consider the race, including others who competed for the Republican gubernatorial nomination this year. That list includes former state House Minority Leader Marty Seifert, state Rep. Paul Kohls and state Sen. David Hann. Other Republicans may throw their hats in the ring, too, including former state Rep. Laura Brod, former state Rep. Brad Finstad, Hennepin County Commissioner Jeff Johnson, businesswoman Susan Marvin and business leader Charlie Weaver.

A couple of wild cards may determine the Republican nomination, however. If Gov. Tim Pawlenty decides to abandon the presidential race for a Senate bid, he would be the prohibitive favorite in the primary. And the state Legislature will be in flux, as everyone in both the House and the Senate will be forced to run following redistricting, so some state lawmakers may be motivated to consider bids for different offices.

Montana

Sen. Jon Tester (D)

Tester will be one of the most vulnerable Democrats in 2012. Insiders familiar with the state said Rep. Denny Rehberg (R), who just won a sixth term, would give Tester his greatest challenge.

As the state’s lone Congressman, Rehberg has run statewide every two years since 2000. He also challenged Sen. Max Baucus (D) in 1996, before being elected to the House. Republican businessman Steve Daines announced his candidacy last week, attempting to tie Tester to President Barack Obama and the new health care law. Republican national security expert Neil Livingstone, told Roll Call he also wants to run.

Tester entered the Senate in 2006 on a margin of fewer than 4,000 votes by targeting the ethical issues surrounding then-Sen. Conrad Burns (R). Republicans have listed this state as their top target for 2012. Tester had more than $500,000 in the bank at the end of September.

New Jersey

Sen. Bob Menendez (D)

Menendez will not serve another term as chairman of the Democratic Senatorial Campaign Committee, a decision that allows him to focus on a re-election bid that could be more challenging than some might think.

Republicans are at a significant voter-registration disadvantage in the Garden State, but the largest voter group isn’t affiliated with either party. Should the anti-incumbent movement from this year persist, Menendez’s lifetime in public service could be a liability in 2012.

A Quinnipiac University poll released last week suggests Menendez has cause for concern. Just 38 percent of New Jersey voters approve of his job performance, compared with 41 percent that disapprove, leaving more than 20 percent undecided. That should be encouraging news for the local GOP, which has yet to find a challenger.

People to watch include Lt. Gov. Kim Guadagno, 2006 Menendez opponent and current state Senate Minority Leader Tom Kean Jr., and even former CNN anchor Lou Dobbs, among others.

Regardless of the opponent, Menendez will have the advantage. He knows how to win an election, having served in Congress since 1993. And he has a healthy cash reserve, reporting $2.3 million in his campaign account at the end of September.

North Dakota

Sen. Kent Conrad (D)

The defeat of Conrad in 2012 would be the culmination of North Dakota Republicans’ efforts over more than two decades to flip the state’s federal offices. Conrad is the only Democrat left in North Dakota’s Congressional delegation, which had been entirely Democratic since 1987. Gov. John Hoeven (R) won a landslide Senate victory and will replace retiring Sen. Byron Dorgan (D). State Rep. Rick Berg (R) defeated Rep. Earl Pomeroy (D).

The list of potential Conrad challengers reflects the deep bench Republicans have built in North Dakota. After Hoeven’s election to the Senate, Lt. Gov. Jack Dalrymple will become acting governor. Dalrymple will appoint former U.S. Attorney Drew Wrigley to replace him as lieutenant governor. In 1992 when he was a state Representative, Dalrymple lost the special election for Senate to Conrad after Democratic Sen. Quentin Burdick’s death.

Other potential Republican candidates include Attorney General Wayne Stenehjem, Bismarck Mayor John Warford and Dickinson Mayor Dennis Johnson.

Ohio

Sen. Sherrod Brown (D)

A magnifying glass will be on Ohio in 2012, when President Barack Obama and his GOP opponent are sure to spend money and manpower on the key electoral state. Brown will be running his first re-election bid. He was active in the 2010 cycle, helping multiple Democrats who lost their House seats, Senate candidate Lt. Gov. Lee Fisher and defeated Gov. Ted Strickland. Brown has a $1.4 million campaign war chest.

Being floated as potential challengers are Rep. Jim Jordan, considered a GOP rising star, and Lt. Gov.-elect Mary Taylor. A dark horse contender is former Sen. Mike DeWine, whom Brown unseated in 2006. DeWine was just elected attorney general.

Depending on his challenger, Brown will likely be considered among the more vulnerable Democrats in a tough cycle for the party. In 2010, Republicans won the governorship and made major gains in the state Legislature, and former Rep. Rob Portman (R) trounced Fisher in the open-seat Senate race.

Pennsylvania

Sen. Bob Casey (D)

Casey is among the Democratic incumbents in Democrat-leaning states who should be safe in 2012. But if the recent cycle taught us anything, it’s that few Democrats are safe in a cycle where the national environment trumps local concerns.

In many states, downballot Democrats like Casey are expected to benefit from President Barack Obama’s place atop the ballot. But Pennsylvania, which features a substantial Democratic voter registration advantage, is not one of them — at least right now. Just 42 percent of Pennsylvania voters would have re-elected Obama if the election were held last week, according to a Public Policy Polling survey released Nov. 9.

The anti-abortion-rights Casey reported just $872,000 in his campaign account at the end of September, a number that might not be enough to scare off a Democratic primary challenger, never mind a Republican opponent.

No one has stepped forward yet, but potential candidates have expressed interest to the state GOP chairman. Those to watch include Rep. Charlie Dent, a moderate Republican just elected to his fourth term in Congress. Rep. Jim Gerlach has also demonstrated an interest in statewide office, and state Rep. Mike Turzai of the Pittsburgh area has been in the conversation as well.

Rhode Island

Sen. Sheldon Whitehouse (D)

Whitehouse rode a Democratic wave to the Senate in 2006, ousting popular moderate GOP Sen. Lincoln Chafee in a race that was largely decided by party affiliation.

Rhode Island voters may have shown some buyer’s remorse, putting Chafee into the governor’s office in 2010. And there’s reason to believe Whitehouse will have to work for another term, even in deep-blue Rhode Island.

His rants against the tea party from the Senate floor fired up the small but vocal Ocean State conservative base. He reported the moderate sum of $576,000 in his campaign account at the end of September, and his unfavorables have hovered around 50 percent for much of the last year.

Whitehouse’s saving grace, for now, is that Republicans will struggle to find a legitimate challenger in a state where Democrats control virtually the entire state Legislature, Congressional delegation and every statewide office.

State GOP Chairman Giovanni Cicione is seriously considering a run, but he’s the first to admit he is a weak candidate, having little personal wealth and having never held elected office.

Whitehouse’s biggest threat could come from term-limited Gov. Donald Carcieri, who will leave office in January 2011. He has deep pockets and better name identification than any other Republican in the state.

Other names to watch include Warwick Mayor Scott Avedisian and Cranston Mayor Allan Fung. Ultimately, Whitehouse should be fine, especially sharing a ballot with a president whose favorable rating is still in the mid-50s here.

Virginia

Sen. Jim Webb (D)

Webb is one of the biggest mystery candidates in a state that was trending toward the Democrats but that swung back in GOP favor in the most recent cycles. Webb won’t say whether he’s running for a second term. He had $471,000 in the bank as of Sept. 30 and even though he notoriously hates to campaign, Webb has been active in helping Democrats this year, doing at least one event with each member of the party’s delegation and helping raise money for them through his political action committee.

In 2006, Webb unseated Republican Sen. George Allen by 9,329 votes of 2.3 million cast, delivering the Senate to the Democrats. Allen is flirting with a rematch, and his office won’t say his timeline for making a decision. But Allen, a former governor, has remained active, campaigning for Republicans this fall. Should Allen run, he’d be the clear favorite. But if he opts against a second try for his old seat, expect Republicans to look to incoming Majority Leader Eric Cantor, Rep. Randy Forbes or former Rep. Tom Davis.

Webb spokesman Will Jenkins said his boss is “giving the matter proper thought and consideration” before announcing his intentions. But Webb sent a signal to supporters recently by granting an interview to the conservative-leaning Real Clear Politics, telling a reporter that he’d warned President Barack Obama the health care debate “was going to be a disaster.” A former Republican who served in President Ronald Reagan’s administration, Webb also openly worried about the “transactional nature” of the Democratic party. There’s been some chatter among Virginia’s influential Democratic bloggers that Webb might deserve a primary from the left, talk that picked up after Webb’s team widely distributed the Real Clear Politics article.

Washington

Sen. Maria Cantwell (D)

Armed with money and a well-known name, Republican Dino Rossi fell 4 points short of defeating Sen. Patty Murray (D-Wash.) in a good cycle for Republicans nationwide. So it’s still a little early to find a top challenger to the state’s other Senator, Cantwell.

The top Republican challenger could be Attorney General Rob McKenna, whom one GOP strategist in the state called the “great hope.” However, he is believed to be eyeing a gubernatorial run in 2012.

Republicans whose names will be discussed include Reps. Dave Reichert and Cathy McMorris Rodgers, as well as tea party favorite Clint Didier, a former Washington Redskins tight end who failed to advance past this year’s Senate primary despite earning an endorsement from former Alaska Gov. Sarah Palin.

2006 ended up being a relatively easy re-election for Cantwell, who at first faced a serious primary challenge from the left but managed to fend off the best-known candidate and hire him to work for her campaign.

Wisconsin

Sen. Herb Kohl (D)

Kohl may take Republican Ron Johnson’s punishing win over fellow Democratic Sen. Russ Feingold as a warning. Kohl, 75, has said he’ll make a decision about whether to run for re-election in the next few months. He had just $26,000 in the bank as of Sept. 30, a sign he might be looking toward retirement after four terms.

A number of Republicans may consider running, whether Kohl decides to retire or not. Though Republican Rep. Paul Ryan has long been suspected of having Senate ambitions, he may be more inclined to stay in the House now that he stands to chair the Budget Committee. However, Ryan is term-limited by House GOP rules and would need to seek a waiver to keep the budget gavel beyond 2012. If he doesn’t run, state Rep. Mike Huebsch has been mentioned, as have previous Senate candidates, including 2006 nominee Tim Michels.

Rep. Ron Kind, who barely won his re-election bid in 2010, has been mentioned as a Democrat who might run if Kohl decides to retire.

Leans Republican

Maine

Sen. Olympia Snowe (R)

Snowe’s greatest threat in 2012 will likely come from the right.

Having already served three terms in the Senate, the moderate Republican enjoys overwhelming popularity statewide and a healthy bank account. A late October survey set her approval rating at 56 percent, and she reported $1.2 million in the bank as of Sept. 30.

But if there’s one lesson from the 2010 cycle, it’s that moderate Republicans are susceptible to tea-party-backed primary attacks. Local tea party activists have already vowed to knock off Snowe. And it’s likely that a conservative with decent name recognition could tap into the national stream of conservative energy (and money) to launch a legitimate primary attack.

A September survey conducted by the Democratic firm Public Policy Polling suggests that Snowe’s safest bet may come from a run as an Independent.

Just 39 percent of likely Republican primary voters approved of her job performance, and 64 percent said she was too liberal. When asked if they would support Snowe or a more conservative challenger, 63 percent of those surveyed selected the generic challenger.

This very well could turn into a replay of the 2010 Delaware race, where a tea-party-backed conservative knocked off a popular moderate in the Republican primary, essentially handing the seat to the Democrat in the general election.

The question, however, is whether Maine Democrats will find a credible challenger to take advantage of the situation.

Most are waiting to see how Snowe, first elected in 1994, proceeds. But keep an eye on Rosa Scarcelli. She lost a crowded Democratic gubernatorial primary but earned respect as a smart, young candidate with a strong business background.

Likely Democratic

California

Sen. Dianne Feinstein (D)

For now, expectations in the state are that Feinstein will run for a fourth full term. While speaking at a campaign event last month for Sen. Barbara Boxer (D), the Los Angeles Times reported, Feinstein let it slip that she plans to run again in 2012, when she will turn 79.

Other Democrats like Lt. Gov.-elect Gavin Newsom and Los Angeles Mayor Antonio Villaraigosa could be interested should she opt out. But the more pressing question is which Republicans will step forward after a strong challenge to Boxer by Carly Fiorina ended up unsuccessful, despite heavy spending from the national party in a GOP wave cycle.

Republicans with known statewide ambitions are considering running, according to GOP strategists in California. They include state Insurance Commissioner Steve Poizner, a former Silicon Valley businessman who lost this year’s gubernatorial primary to Meg Whitman, and Rep. Darrell Issa, who has previously run for governor and Senate and will soon be taking over the House Oversight and Government Reform Committee.

Meanwhile, Fiorina and Whitman remain possibilities.

Hawaii

Sen. Daniel Akaka (D)

Age was an issue for Akaka in 2006, when he faced a Democratic primary challenge from then-Rep. Ed Case. Akaka will be 88 years old by Election Day 2012, but he has told local reporters he will run for a fourth full term.

Any potential GOP challengers will be waiting to see whether outgoing Republican Gov. Linda Lingle decides to challenge Akaka. Lingle, who was term-limited, told the Star-Advertiser that she will “rest” for six months before making a final decision.

New York

Sen. Kirsten Gillibrand (D)

Gillibrand cruised in her 2010 special election, beating Republican Joseph DioGuardi by 26 points in a cycle that largely favored the GOP in New York and across the nation. It’s hard to imagine she will struggle in more favorable conditions in 2012.

Local Republicans aren’t hopeful. They quietly acknowledge they will have a hard time convincing well-known members of the new Republican House majority to give up guaranteed influence for a shot at the Senate.

Their top pick would be Rep. Peter King, who is expected to assume the chairmanship of the Homeland Security Committee. There are a host of second-tier candidates in the ranks of the Empire State’s county executives. Candidates such as Jay Townsend, who fell to Sen. Charles Schumer in 2010, could re-emerge.

Don’t expect a comeback from Carl Paladino, however. New York Republicans believe their 2010 gubernatorial candidate is too polarizing to win statewide office.

Likely Republican

Indiana

Sen. Dick Lugar (R)

Lugar, who will turn 80 in 2012, has committed to running again, and following former Republican Sen. Dan Coats’ resounding win over Democratic Rep. Brad Ellsworth, the early bet is that he would win. His office said its polling shows his favorable ratings in the high 60s, and he had nearly $2.4 million in cash on hand at the end of September.

A Lugar loss might be more likely in the primary than in the general election, as some Indiana Republicans see him as too close to President Barack Obama. Tea party groups have complained about his voting record on Supreme Court nominees and other issues, and National Republican Senatorial Committee Chairman John Cornyn admitted he wants to stave off intraparty challenges to Senators including Lugar.

Lugar, the former mayor of Indianapolis, had no Democratic challenger in 2006 and trounced a Libertarian challenger. Potential Republican challengers include state Sen. Mike Delph, state Treasurer Richard Mourdock and Don Bates Jr., who lost the 2010 Republican primary to Coats. A split primary, however, may clear the way for Lugar to win easily.

There are credible potential Democratic challengers. Ellsworth and fellow outgoing Rep. Baron Hill, both of whom have run statewide, could run, as could Rep. Joe Donnelly. Donnelly squeaked out his re-election bid in northern Indiana but is likely to end up in a more hostile district after redistricting. Tim Roemer, the former Indiana Congressman and current ambassador to India, is also mentioned as a strong potential candidate.

Tennessee

Sen. Bob Corker (R)

Corker, whose 2006 win against then-Rep. Harold Ford Jr. was a bright spot for Republicans as the party lost the Senate, will seek re-election in what could be an easy race given the beating Tennessee Democrats took this month.

But tea party activists have been targeting Corker, protesting at his office and calling him a “Republican in name only” whom they’d like to see defeated. Corker loyalists dismissed primary potential as inside-the-Beltway chatter. A GOP firm’s June poll of Republican primary voters found Corker in good standing with the GOP and even with a 72-percent approval rating among voters who identify with the tea party and who would attend a tea party rally.

Corker has been hosting town halls to explain his role in financial reform and to pitch his ideas for capping spending and stopping additions to the deficit, an aide said.

Tennessee Democrats admitted they remain shell-shocked after losing three House seats, 14 state House seats and the governor’s mansion in the midterm election. Outgoing Gov. Phil Bredesen is the Democrats’ preferred candidate, but he’s given no indication he’s interested in running for Senate. His office declined to comment. A Republican source noted that Corker and Bredesen have been friends for years since working together in the mid-1990s to bring the Houston Oilers to Tennessee.

Other potential candidates could be retiring Democratic Reps. Bart Gordon and John Tanner or defeated Democratic Rep. Lincoln Davis. State Sen. Roy Herron, who lost his bid for Tanner’s seat, also could run statewide.

Safe Democratic

Delaware

Sen. Tom Carper (D)

There’s little reason to expect the fireworks of 2010’s Senate race in the First State to resurface in 2012. Carper is expected to run for a third term, and he’s expected to win.

Yes, the now-famous tea-party-backed Christine O’Donnell has not ruled out a fourth Senate bid. But she was underwhelming in 2010, losing by 16 points to a little-known county executive, even after raising millions of dollars from conservatives across the country.

The popular Republican Rep. Mike Castle, who lost the GOP Senate primary to O’Donnell and will be out of politics in January for the first time in three decades, isn’t likely to challenge Carper, a longtime ally. And allegiances aside, Castle will be 73 years old the next time Delaware voters head to the polls.

Delaware Republicans aren’t known for having a deep bench, and in fact, lost seats in their state House in 2010.

But keep an eye on deep-pocketed attorney Michele Rollins. She lost the 2010 GOP primary for the state’s at-large House seat to a more conservative candidate, and she could emerge as a challenger.

Maryland

Sen. Benjamin Cardin (D)

Cardin is another member of the class of 2006 but unlike some of his colleagues, Cardin is running in one of the most Democratic states in the country and few if any Republican names are being floated as potential challengers.

In his first election, Cardin defeated Michael Steele, then the lieutenant governor and now the Republican National Committee chairman, by 10 points. This year, a tough cycle for Democrats almost everywhere, both Gov. Martin O’Malley (D) and Sen. Barbara Mikulski (D) cruised to re-election.

Maryland has not elected a Republican Senator since 1980.

New Mexico

Sen. Jeff Bingaman (D)

Bingaman has yet to announce his plans for 2012, but his recent actions indicate to Democrats in the state that the 67-year-old will be running for a sixth term.

One Democratic insider said Bingaman held his first fundraiser since 2006 in September, when he raised a few hundred thousand dollars, and he has another one scheduled in the state next month. He had $516,000 in the bank as of Sept. 30. Bingaman was also active on the trail this year for local, state and federal Democrats.

Much of the chatter over who will challenge Bingaman is centering on former Rep. Heather Wilson. The Albuquerque Republican, who lost in the 2008 Senate primary, is currently serving as chairwoman of the transition team for Gov.-elect Susana Martinez, and party insiders on both sides said she is seriously considering a bid.

Already in the race is Bill English, a businessman who briefly ran for the House in 2001.

Safe Republican

Arizona

Sen. Jon Kyl (R)

The Senate Minority Whip is expected to run for a fourth term in 2012. Democrats failed to put forth a top-tier challenger against Sen. John McCain (R) in 2010, and at this point it is unclear if any will step forward against Kyl, who has won re-election fairly easily. However, a Democratic source suggested the state would be among the party’s prime targets given that President Barack Obama will try to win the state in 2012.

The top name being discussed to challenge Kyl is Rep. Gabrielle Giffords, who just held off a tough GOP challenge in her Tucson-based district. Other possibilities in the Republican-leaning state include Reps. Ann Kirkpatrick and Harry Mitchell, who were both just defeated for re-election. Also mentioned by insiders was Jon Hulburd, an attorney who lost to Rep.-elect Ben Quayle (R) but was said to have run a great field operation.

Mississippi

Sen. Roger Wicker (R)

Wicker (R) plans to seek re-election and has already been barnstorming the state to shore up support. Wicker was appointed by Gov. Haley Barbour (R) after Sen. Trent Lott (R) stepped down. Wicker won a 2008 special election to serve the remainder of Lott’s term.

A Wicker spokesman said the 2011 statewide elections to replace the term-limited Barbour are Mississippi’s primary focus, and he believes a Democratic candidate will emerge to challenge Wicker in early 2012.

This race is expected to be an easy one for Republicans since Mississippi Democrats lost seats this month, leaving Rep. Bennie Thompson as the only Democrat in the delegation.

Texas

Sen. Kay Bailey Hutchison (R)

The question in Texas is whether Sen. Kay Bailey Hutchison will run for re-election after losing her primary bid for governor in 2010. Hutchison irked state Republicans by first saying she would retire and then changing her mind. In 2012, this race is likely to be won in the Republican primary whether or not Hutchison seeks re-election. Republican Elizabeth Ames Jones, a railroad commissioner, has already opened a federal campaign account to seek the nomination, and former Secretary of State Roger Williams also has his campaign under way.

The number of Democrats who could credibly run for statewide office in Texas is small and shrinking after the 2010 cycle. Former Houston Mayor Bill White, who lost his 2010 gubernatorial bid to Gov. Rick Perry (R), already has declined to run for Senate in 2012. Democratic Reps. Chet Edwards and Ciro Rodriguez, who lost their re-election bids, will have options in 2012, including the Senate race and additional Congressional districts following redistricting.

Utah

Sen. Orrin Hatch (R)

Hatch is a top candidate for a Republican primary after Sen. Bob Bennett was defeated at the state party convention in May. The most likely top-tier challenger is Rep. Jason Chaffetz, an up-and-comer in the House GOP caucus who just won a second term.

Chaffetz already has a record. He came to Congress by ousting sitting Rep. Chris Cannon (R) in a primary, and he has hinted openly that he is considering running against Hatch.

As it was with the 2010 Senate race, the fireworks may all take place in the primary. Rep. Jim Matheson is the top Democrat in the state to watch, but he will have a tough time of it given Utah’s strong Republican leanings.

Wyoming

Sen. John Barrasso (R)

Unless a credible primary challenger emerges, Barrasso will likely be elected to a full term in 2012. Wyoming has not elected a Democrat to the Senate since 1970, and Barrasso won the 2008 special election with 73 percent of the vote.

Outgoing Gov. Dave Freudenthal would be the top Democratic challenger in the race if he decides to run, though that possibility is believed to be a long shot at this point.

Safe Independent

Vermont

Sen. Bernie Sanders (I)

While he is in his first term, Bernie Sanders has been a fixture in Vermont politics for decades, and there’s little sign he’s in danger of losing his seat in 2012.

Sanders’ outspoken style and political leanings — he is a self-described socialist, elected as an Independent, who caucuses with Democrats — might put him in a weaker position in another state. His fundraising has been underwhelming to date: He reported just $111,000 in his campaign account at the end of September.

But Republicans aren’t known for their deep bench in Vermont. State Auditor Tom Salmon has been discussed as a challenger, but it’s a big jump from the state’s top accountant to U.S. Senator.

— Compiled by Kyle Trygstad, Tricia Miller, Steve Peoples and Christina Bellantoni