What's at stake: In their quest to reclaim the majority, House Democrats are fighting history: the chamber's majority has not changed hands during a presidential election in 60 years. Moreover, not since Ulysses S. Grants' re-election in 1872 has a president won a second term and have his party gain 25 or more seats in the House, which is what Democrats need to retake the majority. Republicans hold 242 seats, Democrats 193. Here are some of the tossup races to watch:
2nd District: Rep. Democrat David Cicilline has had problems, but he registered a convincing primary win, and has in recent polls turned a 15-point deficit in February into a 44 to 38 percent lead over Republican nominee Brendan Doherty in a Democratic district.
41st District: Democrat Mark Takano is a slight favorite against GOP Riverside County Supervisor John Tavaglione in this Democratic-leaning district.
47th District: There's little sign right now that state Sen. Alan Lowenthal, D, is in trouble, despite some GOP hype surrounding Long Beach City Councilman Gary DeLong, R.
26th District: Rep. David Rivera, R, is being left for dead by some in the local GOP, and Sen. Marco Rubio, R-Fla., hasn't done much to defend his friend. A recent survey by a GOP-leaning pollster showed him trailing Democrat Joe Garcia by 10 points.
2nd District: Rep. Steve Southerland's, R, district appears to have taken a turn for the competitive, with both sides spending money there in recent days. A Democratic poll last week showed Southerland and former state senator Al Lawson, D, tied.
10th District: Rep. Daniel Webster, R, suddenly finds himself in a tight race against Democrat Val Demings, the former Orlando Police chief.
2nd District: Rep. David Loebsack, D, has emerged as a GOP target, with the GOP spending about half a million dollars against him. He is opposed by Republican John Archer.
8th District: National Democrats have pulled out of this race, leaving Rep. Larry Kissell to fend for himself against Republican Richard Hudson in a district that is significantly more Republican after 2010 redistricting. Republicans are favored to win three Democratic-held seats in North Carolina, and Rep. Mike McIntyre, D-N.C., could be in trouble too.
2nd District: Republican Markwayne Mullin is a strong favorite for the seat being vacated by retiring Rep. Dan Boren, D.
2nd District: Another likely GOP pickup comes in this seat being vacated by Democratic Senate nominee Rep. Joe Donnelly. Republican Jackie Walorski appears positioned to win.
6th District: Rep. Jim Gerlach, R, is always a target, but his polling has him up by a huge margin. Democrats haven't spent money to help Manan Trivedi in the Democratic-leaning district.governor
The most closely watched contest is in North Carolina, where Democrats could lose the governor's mansion for the first time in two decades. Tainted by an ethics investigation, Gov. Beverly Perdue, D, opted not to run, and Lt. Gov. Walter Dalton, D, is trailing Republican Pat McCrory, said statewide polls.
Three former House members are hoping to become governors. In Indiana, ex-Rep. Mike Pence, R, is running against Democrat John Gregg to succeed Gov. Mitch Daniels, R. In Washington, ex-Rep. Jay Inslee, D, narrowly leads state Attorney General Rob McKenna, R, and in Montana, ex-Rep. Rick Hill, R, faces state Attorney General Steve Bullock, D, in a contest to succeed the term-limited governor, Brian Schweitzer, D. Other races: West Virginia, New Hampshire, Delaware, Missouri, North Dakota, Utah and Vermont.
What's at stake: Democats hold a 53-47 advantage in the Senate, counting the two independents and must defend 23 seats to the GOP's 10. The Republicans need a net of four seats to grab the majority if President Obama wins and a net of three if Romney captures the White House and his running mate, Paul Ryan, would break a Senate tie as vice president.
Polls show former surgeon general Richard Carmona, a Democrat, in a close race with GOP Rep. Jeff Flake in the red state. Carmona, who was surgeon general under President George W. Bush. was recruited by President Obama. Flake is a fiscal conservative who has earned a reputation of bucking his party.
Independent former governor Angus King started this race as the heavy favorite. But negative GOP ads against King have moved Republican GOP Secretary of State Charlie Summers into serious contention.
This one is really close. Former state Attorney General Heidi Heitkamp has turned into one of the best Democratic recruits of the year, putting in play a state that was thought to be solidly in the GOP's column. The GOP nominee, freshman Rep. Rick Berg isn't getting such sterling reviews.
The shape of this race has changed in recent weeks, with polling showing Democrat Tim Kaine jumping to an 8-point lead over former Sen. George Allen. The GOP plan to attach Kaine to Obama has paid limited dividends thus far.
This has been close from the beginning and is expected to stay that way. Sen. Jon Tester, D, and Rep. Denny Rehberg, R, have always been within a few points of each other. Republicans have tried to tie Tester to Obama, while Democrats have attacked Rehberg as a lobbyist and for suing his local fire department after a wildfire damaged his property.
Richard Mourdock's upset of Sen. Richard Lugar in the state's GOP Senate primary opened the door for Democrats in a state that is expected to go Republican at the presidential level. Rep. Joe Donnelly, D, has won in a tough House district before. If the GOP lose this one, they may also lose their majority hopes.
The country's most high-profile Senate race pits former Obama adviser and liberal hero Elizabeth Warren, D, against Sen. Scott Brown, R, a popular senator with a moderate, every-man vibe. For a while, Brown's appeal seemed to be winning the day. But this is Massachusetts, and his party affiliation is a liability. Recent polls show Warren with a small edge.
Former GOP Governor Tommy Thompson's attempted political comeback had been looking good. He survived a tough primary and was leading Democrat Rep. Tammy Baldwin in early polls. But as Obama has risen in the polls here, so has Baldwin. Look for Republicans to focus on Baldwin's record as one of the most liberal members of Congress.
Appointed Sen. Dean Heller, R, appears to be a slight favorite to retain the seat forfeited by disgraced former Sen. John Ensign, R. But Nevada is a presidential swing state, and Democratic nominee Shelly Berkley is a favorite of Senate Majority Leader Harry Reid, who will do plenty to help her down the stretch.
Linda McMahon, R, is a different candidate from two years ago when she lost another open-seat contest by double digits. Almost every recent poll shows a close race with Rep. Chris Murphy, D, despite Connecticut's Democratic tendencies. But for McMahon, whose wrestling empire has been tainted by scandal, the game is to build a personal brand separate from her wrestling identity.