Republican incumbent Steve King's bid for a sixth term in Congress will be his toughest. King won re-election in his old western Iowa district with 66% of the vote in 2010, and he's never dipped below 59% in any of his previous races. This year, he faces a new district and a tough new challenger in Democrat Christie Vilsack, Iowa's former first lady and the wife of U.S. Agriculture Secretary Tom Vilsack. The good news for King is that his enormous new district in the northwest part of the state is comprised mostly of counties won by John McCain in 2008. King has had a fundraising advantage over Vilsack. But Vilsack is the strongest possible candidate Democrats could have fielded. She has been competitive financially. The political makeup of the district is still a bit of a reach for a Democrat.

Louisiana 3: Rep. Charles Boustany (R) vs. Rep. Jeff Landry (R)

Merged district

As in California, redistricting and a "top-two" primary system have forced two incumbent lawmakers of the same party into a November showdown. Republican Charles Boustany, a surgeon elected in 2004, faces freshman Republican Jeff Landry, an attorney and businessman, former police office and tea party favorite. Boustany represents significantly more of the new district than Landry, but the freshman proved he is capable of pulling off surprises when he defeated the better-known former Louisiana House speaker in the 2010 primary. Under state law, the November election will serve as an open primary, in which the top two finishers will advance to a December runoff if no one gets a majority.

Maryland 6: Rep. Roscoe Bartlett (R) vs. John Delaney (D)

By all accounts, Republican Roscoe Bartlett's bid for an 11th term appears to be his last. The long-time western Maryland representative was a top target for Democrats who redrew the district last year. As a result, his once-safe seat now stretches from the state's westernmost point to include a sizable piece of heavily Democratic Montgomery County and now reaches almost to the District of Columbia border. His Democratic opponent is John Delaney, a wealthy businessman. Delaney pulled an upset in the Democratic primary over Rob Garagiola, a state senator with a string of endorsements from party establishment-types, including Gov. Martin O'Malley. Bartlett has little hope of pulling out a miracle.

Massachusetts 4: Joe Kennedy III (D) vs. Sean Bielat (R)

Open Democratic-held seat

When Democratic Rep. Patrick Kennedy of Rhode Island left office in January 2011, it ended his family's 64-year streak of service in Congress that began with the swearing-in of freshman congressman John F. Kennedy. In 2012, Democratic congressional candidate Joe Kennedy III, grandson of Robert F. Kennedy, hopes to begin a new streak by replacing retiring Rep. Barney Frank in the 4th Congressional District. Kennedy, a former prosecutor and Peace Corps member, is heavily favored to win; no member of his family has ever lost a race in Massachusetts. His opponent is Republican Sean Bielat, a businessman and Marine Corps reservist.

Massachusetts 6: Rep. John Tierney (D) vs. Richard Tisei (R)

Rep. John Tierney is in danger of becoming the first Democrat to lose a U.S. House race in Massachusetts since 1994. The eight-term incumbent has been dogged by a financial scandal involving his wife and her brothers and an illegal gambling operation. The Republican nominee is Richard Tisei, a former state senator who is openly gay. Tierney has been pounded with more than $3 million in ads this cycle from Tisei, the national Republican party and pro-Republican groups, eager to defeat a Democrat in Massachusetts. The district is Democratic but the ongoing scandal appears to have taken a toll. A last September Boston Globe/University of New Hampshire poll had Tisei with 37%, Tierney with 30% and 30% undecided.

Minnesota 6: Rep. Michele Bachmann (R) vs. Jim Graves (D)

Tea party favorite Michele Bachmann was a shoo-in for re-election when she folded up her presidential campaign in January. Ten months later, Bachmann still has the advantage but she faces a tough challenger in Jim Graves, a wealthy businessman. Graves has waged a competitive race in October, spending $1.2 million in TV ads, compared to $1.7 million for Bachmann. The conservative congresswoman has never posted huge numbers on Election Night, but redistricting has made her district slightly more Republican. Defeating a high-profile conservative like Bachmann would be a nice win for Democrats, but she is not at the top of the list of vulnerable Republican incumbents.

Nevada 4: Steven Horsford (D) vs. Danny Tarkanian (R)

New district

There's a competitive race in Nevada's newest congressional district. The nominees are Democrat Steven Horsford, the state senate majority leader, and Republican Danny Tarkanian, a businessman and son of UNLV basketball coaching legend Jerry Tarkanian. The younger Tarkanian was a 2010 U.S. Senate candidate but placed third in the Republican primary. The two candidates have been fairly evenly matched in terms of fundraising as well as the assistance they've received from their national parties and from outside groups in terms of TV ads. The district leans slightly Democratic. The outcome could be affected by competitive races for president and U.S. Senate higher up on the ballot.

New Hampshire 1: Rep. Frank Guinta (R) vs. Former Rep. Carol Shea-Porter (D)

As was the case in 2010, Republican Frank Guinta and Democrat Carol Shea-Porter face off in the battle for New Hampshire's 1st Congressional District. This time, Guinta is the incumbent and Shea-Porter is the challenger. Shea-Porter was elected in the Democratic wave of 2006 and served two terms before losing to Guinta in 2010, 54%-42%. The two are fairly evenly matched in fundraising. The race is competitive. A strong showing by Obama or Romney at the top of the ticket will be an important factor.

New Hampshire 2: Rep. Charlie Bass (R) vs. Ann McLane Kuster (D)

The incumbent is Republican incumbent Charlie Bass faces Ann McLane Kuster. Kuster lost to Bass in the general election in 2010 but is running again. Bass narrowly beat and she has outraised Bass though they started October with roughly the same amount in the bank. The Democrat has far outspent her opponent on the airwaves even though the national Republican party has invested funds on behalf of Bass. A WMUR/University of New Hampshire poll from early October had Kuster at 38%, Bass 35%, with 25% unsure. The district is more Democratic the state's other region, which works in Kuster's favor.

New York 24: Rep. Ann Marie Buerkle (R) vs. Former Rep. Dan Maffei (D)

Rep. Ann Marie Buerkle was elected in the Republican wave of 2010 and now has to defend her seat from the man she defeated. Democrat Dan Maffei, a longtime Capitol Hill staffer, won this upstate New York district in 2008 after it had been in Republican hands for almost 30 years. He lost the seat to nurse and tea party favorite Buerkle in one of the closest House races that year. The two have been evenly matched in both fundraising and TV ad spending. The district now leans slight more Democratic, which doesn't help Buerkle, who only managed to win this seat by about 600 votes.

North Carolina 7: Rep. Mike McIntyre (D) vs. David Rouzer (R)

Democratic Mike McIntyre is running a competitive race despite a newly redrawn district that skews heavily Republican. The Republican nominee is David Rouzer, a state senator. McIntyre, an eight-term incumbent, leads in fundraising and has kept even with ad spending by pro-Republican outside groups and the national Republican party. Rouzer has stayed off the airwaves. Similar to fellow southern Democrat John Barrow in Georgia, McIntyre is showing surprisingly strong signs of life in a district that was essentially drawn to end his career.

Ohio 9: Rep. Marcy Kaptur (D) vs. Samuel "Joe the Plumber" Wurzelbacher (R)