Updated 12:37 a.m. | As Election Day folded into Nov. 7, the only question remaining in the fight for the Senate was the size of the Democratic majority.

Democrats were looking at a net gain of two seats, with just two Democratic-held seats and one Republican seat left to be called. That meant the Democratic majority could be no lower than 53-47, exactly where it was at the beginning of the cycle.

“When we started this campaign, no one, and I mean no one gave us a chance.  But we went out and built the best Senate campaigns in the history of the country,” Democratic Senatorial Campaign Committee Chairwoman Patty Murray (Wash.) said in a statement. “We recruited some of the highest quality candidates, including a record number of women. Democrats never let up, and now we will retain our majority in the United States Senate.”

The Associated Press called the Wisconsin Senate race after midnight, with Rep. Tammy Baldwin (D) topping former Gov. Tommy Thompson (R) for the seat of retiring Sen. Herb Kohl (D). That left two Democratic-held seats yet to be called: in Montana, where Sen. Jon Tester (D) faced Rep. Denny Rehberg (R), and in North Dakota, where former state Attorney General Heidi Heitkamp (D) faced Rep. Rick Berg (R) for the seat of retiring Sen. Kent Conrad (D).

Nevada Sen. Dean Heller (R) was looking to hold on against Rep. Shelley Berkley (D), even as President Barack Obama carried the state.

Updated 11:25 p.m. | Democrats will retain control of the Senate.

Tim Kaine’s (D) victory in Virginia and Sen. Claire McCaskill’s (D-Mo.) re-election took two more pickup opportunities off the map for Republicans and left the GOP without enough states left to complete its quest for the majority.

With the presidential contest now called for President Barack Obama, Democrats would control the Senate even in the event of a 50-50 tie, as Vice President Joseph Biden would cast the deciding vote.

A few outstanding races will decide the final Senate count. Democrats are hoping to defeat Sen. Dean Heller (R-Nev.) and win the open Arizona seat. Republicans are looking to defeat Sen. Jon Tester (D-Mont.) and win the open North Dakota seat.

Democrats have so far picked up seats in Indiana, Maine and Massachusetts. Republicans have picked up the open seat in Nebraska.

Updated 10:21 p.m. | Even as several key states remained too close to call, developments during the past hour made it highly unlikely that Republicans could win a majority in the Senate.

Victories in Massachusetts for Elizabeth Warren and in Indiana for Rep. Joe Donnelly increased to six the number of Democratic seats Republicans would need for a 50-50 tie.

Democrats came into the day with a 53-47 majority. Republicans have now lost three of their own Senate seats: Massachusetts, Indiana and Maine.

Missouri appeared likely to be won by Sen. Claire McCaskill (D), but the Associated Press had not yet called the race. Republicans still have a solid chance of winning in Montana, Virginia, Nebraska, North Dakota and Wisconsin. They also have opportunities in New Mexico and Hawaii, but those are long shots.

Democrats still have two more Republican-held seats they could pick up in Nevada and Arizona.

Donnelly defeated state Treasurer Richard Mourdock, and Warren defeated Sen. Scott Brown in the race for the late Sen. Edward Kennedy’s former seat.

Updated 9:21 p.m. | There were still several races too close to call three hours after the first polls closed and with the battle for the Senate still up for grabs.

However, WWE CEO Linda McMahon’s (R) loss to Rep. Christopher Murphy (D) in Connecticut knocked — along with Florida, Ohio and Pennsylvania — another pickup opportunity off the map for Republicans. Every missed opportunity narrows the GOP’s path to eclipse the Democrats’ 53-47 majority.

Races were still too close to call in Virginia and Massachusetts, and polls in a few more important states closed at 9 p.m. They included the Tossup races in North Dakota and Arizona, two states GOP presidential nominee Mitt Romney will win easily and that were not expected early in the cycle to host competitive Senate races.

Rep. Rick Berg of North Dakota is hoping to add this state to the Republicans’ column. He faced former state Attorney General Heidi Heitkamp (D) for the seat of retiring Sen. Kent Conrad (D). Rep. Jeff Flake (R-Ariz.) is looking to hold the seat of retiring Sen. Jon Kyl (R) in a competitive showdown with former Surgeon General Richard Carmona (D).

Democrats’ ability to keep both races competitive contributed to the changing narrative of the Senate landscape this cycle.

Polls also closed in several other states with varying degrees of competition. In Nebraska, state Sen. Deb Fischer (R) was favored against former Sen. Bob Kerrey (D) in the race for the seat of retiring Sen. Ben Nelson (D). This was Republicans’ best pickup opportunity of the cycle.

Wisconsin is another closely watched open-seat race. Rep. Tammy Baldwin (D) and former Gov. Tommy Thompson (R) were running close in late polls in a state also close in the presidential race.

Rep. Martin Heinrich (D-N.M.) was expected to hold the seat of retiring Sen. Jeff Bingaman (D). Polls for the last two months gave Heinrich a significant advantage against former Rep. Heather Wilson (R), who lost a 2008 bid for Senate.

Races were called in favor of Sens. Amy Klobuchar (D-Minn.), John Barrasso (R-Wyo.), Debbie Stabenow (D-Mich.) and Bob Casey (D-Pa.).

8:11 p.m. | Polls closed at 8 p.m. in two of the most closely watched Senate races in the country, as well as two races that were late entrants to the competitive playing field.

The Republican-held seats in Massachusetts and Maine provided Democrats with their best pickup opportunities this cycle. Former Gov. Angus King (I) won the Senate race in Maine and is expected to caucus with Democrats, but the three-way general election provided for some interesting media strategies from both national party committees. The Associated Press projected him the winner shortly after 8 p.m.

In Massachusetts, Sen. Scott Brown (R) and Harvard Law School professor and consumer advocate Elizabeth Warren (D) engaged in one of the most expensive and competitive races in the country. Along with Maine, the outcome there has considerable ramifications for the GOP’s majority prospects, as a loss would in turn mean the party must pick up yet another Democratic seat.

Brown entered his bid for a full term with the edge, given his ability to win crossover Democrats. But Warren’s national fundraising network coupled with the expectation that President Barack Obama would carry the state handily gave Democrats one of their best offensive opportunities.

The Florida Senate race was called quickly after polls closed at 8 p.m., with Sen. Bill Nelson (D) holding on against Rep. Connie Mack IV (R). Nelson had been solidly favored for a few months, even as the presidential race was tight.

Elsewhere, polls closed in Connecticut and Pennsylvania, where two Democratic-held seats attracted outside spending late in the election cycle. Pennsylvania Sen. Bob Casey (D) faced a wealthy challenger in Tom Smith (R) and a far more competitive race than had been predicted. That state also tightened late in the presidential contest.

In Connecticut, Republican Linda McMahon, the former WWE CEO and the 2010 Senate nominee, against invested considerable personal funds in the race and gave Democrats a scare in a state Obama should win by a wide margin. Still, Rep. Christopher Murphy (D) had the late edge.

Sens. Joe Manchin (D-W.Va.) and Bernie Sanders (I-Vt.) were the first Senators whose re-elections were called. Joining them in the 8 o’clock hour were Sens. Tom Carper (D-Del.), Sheldon Whitehouse (D-R.I.), Bob Corker (R-Tenn.) and Benjamin Cardin (D-Md.).

7:17 p.m. | Democrats entered Election Day with the edge in the battle for the Senate, and a few states with early poll times should give strong clues toward whether the party will hold its majority for another two years.

At 7 p.m. EST all polls were closed in Virginia and Indiana, and polls will close in Ohio at 7:30 p.m. Most polls will have closed in Florida by 7 p.m. as well, but much of the Panhandle allows voting until 8 p.m.

With Democrats currently holding a 53-47 majority, the path for Republicans would narrow considerably if former Virginia Gov. George Allen (R) does not reclaim his former seat in his race against former Gov. Tim Kaine (D).

Meanwhile, GOP hopes would be all but dashed if Indiana state Treasurer Richard Mourdock (R) loses his bid for the open seat after defeating Sen. Dick Lugar in the GOP primary in May. Roll Call rates both races as Tossups.

Allen and Kaine are vying for the seat of retiring Sen. Jim Webb (D), who defeated Allen in 2006. The race is inextricably tied to the presidential contest, which was also a Tossup in the closing days of the campaign.

Mourdock faces Rep. Joe Donnelly (D) in a surprisingly competitive race that took a turn for the worse for Republicans following the primary. Some late polls gave Donnelly the lead, but this is a state that GOP presidential nominee Mitt Romney should win by a significant margin.

In Ohio, Sen. Sherrod Brown (D) is favored in his first bid for re-election. Republicans are counting on a strong showing from Romney in one of the most important presidential contests to help push state Treasurer Josh Mandel (R) over the finish line.

Several more close contests will still be to come after the 7 o’clock hour, but these three races can set the tone and give political observers a taste of what’s to come.