Sixteen months removed from the 2006 midterm elections, the heads of the Democratic and Republican Senate campaign committees are bullish on their party’s ability to pick up seats, although they face different challenges in getting there.

For Republicans, the hope of expanding their current 55-seat majority could hinge on the party’s ability to convince a handful of top-tier candidates to run against entrenched incumbents.

Democrats, meanwhile, have almost the opposite problem and their formula for success rests largely on their ability to prevent at least four contested primaries from becoming damaging bloodbaths that hamper the eventual nominee’s November prospects.

Beyond specific races, both National Republican Senatorial Committee Chairwoman Elizabeth Dole (N.C.) and Democratic Senatorial Campaign Committee Chairman Charles Schumer (N.Y.) believe the national political dynamic will favor their party come 2006.

While acknowledging in an interview Friday that the 2006 cycle — coming in the sixth year of President Bush’s tenure — presents natural obstacles for the GOP, Dole said voters will tire of Democrats’ obstructionism. What’s more, she argued that the Democratic Party’s embrace of liberal groups such as MoveOn.org sends the wrong message to voters.

“MoveOn seems to be calling the shots,” Dole said.

That point was buttressed by an e-mail update to supporters Friday signed by NRSC Executive Director Mark Stephens. He claimed that “the George Soros/Howard Dean/Michael Moore/MoveOn.org element of the Democratic Party has taken an increasingly prominent role in determining the legislative strategy and political rhetoric of the Democrat Leadership in the U.S. House and Senate.

“Mainstream Democrats ought to wake up and smell the coffee,” Stephens wrote. “Their party has been compromised by the extreme left. The extreme left is supplying much of the money and the grass roots volunteers that feed the Democrat political machine. Republicans need to understand as well because that money and political organization is pointed straight at the mid-term elections in 2006. We need to be ready.”

But Schumer said in a recent interview that it is the Republicans who have been captured by the extremists. He argued that voters who have been leaning to the GOP in recent elections have been turned off by Republican leaders’ hard line positions this year on Bush’s judicial appointments and the Terri Schiavo case and are now poised to return to the Democrats.

“The public is sensing a whiff of extremism in the air,” Schumer said, adding that working class voters and “mainstream” Republican Protestants are being turned off by the GOP.

Beyond the national trends and the charges and counter-charges of extremism, what is happening in the states could ultimately determine which party gains seats in the Senate in 2006.

The Democrats have competitive multi-candidate primaries on tap in Maryland, Minnesota, Montana and Rhode Island next year — all states where Republicans either have an incumbent or have essentially cleared the field for their desired nominee.

Both Maryland and Minnesota are open seats that Democrats are defending, while the DSCC has made defeating Sens. Conrad Burns (R-Mont.) and Lincoln Chafee (R-R.I.) a top priority this cycle.

In Rhode Island, Secretary of State Matt Brown and former state Attorney General Sheldon Whitehouse are vying for the chance to take on Chafee, who could face a competitive primary challenge of his own.

Democrats had hoped to woo Rep. James Langevin into the race but he took a pass earlier this year.

Similarly, in Montana, state Senate President Jon Tester and state Auditor John Morrison are competing for the right to challenge Burns.

The DSCC has urged its candidates to run clean campaigns.

“The DSCC is sending a message to the primary campaigns to keep their efforts focused on their GOP opponents and not one another,” DSCC spokesman Phil Singer said.

In Minnesota, Hennepin County Attorney Amy Klobuchar and child safety advocate Patty Wetterling, who are running to succeed retiring Sen. Mark Dayton (D-Minn.), have — to the relief of the DSCC — agreed to abide by the results of the Democrat-Farmer-Labor state convention and won’t contest the nomination to the primary. Still, wealthy developer Kelly Doran has not yet made that same pledge.

In Maryland, Rep. Benjamin Cardin and former NAACP president Kwesi Mfume are already seeking the Democratic nomination in the open seat race and other candidates, including Rep. Chris Van Hollen (D), could still jump in.

Maryland currently has a Sept. 12, 2006, primary, but the Democratic-controlled state Legislature is contemplating moving the date to June 20 — in part to give the party’s nominees extra time to heal any wounds from a contentious primary.

At the same time, Senate Republicans are focusing their efforts on getting top-tier challengers to run against incumbents in North Dakota, Michigan and West Virginia.

North Dakota Gov. John Hoeven (R) and Rep. Shelley Moore Capito (R-W.Va.) represent the party’s only real shot at competitive challenges to Democratic Sens. Kent Conrad and Robert Byrd, respectively. Both have said they are considering running.

Schumer expressed confidence that Byrd will prevail whether or not Capito is his challenger.

“The magic has not faded one jot,” Schumer said. “I think anyone who runs against him does it at his or her own peril.”

In Michigan, Republicans hope that Dominos Pizza CEO Dave Brandon will decide to run against first-term Sen. Debbie Stabenow (D). The party’s top choice, Rep. Candice Miller (R), said no to a Senate bid earlier this year.

Party leaders are also encouraging Florida House Speaker Allan Bense (R) to run for the seat currently held by Sen. Bill Nelson (D-Fla.). Rep. Katherine Harris (R) has said she is running but many in the party establishment believe she is such a polarizing a figure that she would be unable to win a general election.

Democrats have a clear edge when it comes to early candidate recruitment this cycle — with Pennsylvania Treasurer Bob Casey Jr.’s (D) decision to challenge Sen. Rick Santorum (R-Pa.) their crowning achievement.

Republicans, meanwhile, appear to have scored a big victory with Maryland Lt. Gov. Michael Steele’s (R) decision to form an exploratory Senate committee. But at the same time, the NRSC has been dealt recruiting setbacks in Nebraska, Washington, Vermont and Michigan, where top candidates decided to forgo bids.

Democrats are still hopeful top-tier challengers will emerge in Ohio and Missouri, believing that Sens. Mike DeWine (Ohio) and Jim Talent (Mo.) are vulnerable.

The party’s prospects for a competitive race against Sen. Jon Kyl (R-Ariz.) recently skyrocketed, now that millionaire state Democratic Party Chairman Jim Pederson is expected to run.

Schumer touted the current standing of the Democratic Senators who are up next year.

“Every incumbent Democrat is a frontrunner,” Schumer said. “I would not say that about the Republicans.”

Santorum and Chafee top the list of vulnerable incumbents, while the Democratic open seat race in Minnesota is widely regarded as a toss up.

Republicans, meanwhile, tout the fact that they are only defending one open seat (Tennessee) while Democrats are defending three. And they point to the recent trend of Republicans winning open seat races in the South to illustrate their belief that they will hold onto the seat of retiring Sen. Bill Frist (R).

Still, Republicans face a potentially bloody primary in the Volunteer State — their only competitive primary so far this cycle — while Rep. Harold Ford Jr. is considered the likely Democratic nominee. Ford would become the first black Senator elected from the South if he wins.

But unlike last cycle, when Democrats lost control of five seats in the South, Schumer noted that the other open-seat battlegrounds (Vermont, Maryland and Minnesota) are all Democratic-friendly territory.

“The blue states are going to get bluer in ’06,” he said.