Georgia 12: Rep. John Barrow (D) vs. Lee Anderson (R)

Democratic incumbent John Barrow is fighting for his political life in this heavily Republican district, which is far better than Republicans had expected would be the case at this point when they drew the district's boundaries. According to an analysis by the Cook Political Report, President Barack Obama's 2008 vote in Barrow's new district is 44%, compared with 55% under the old lines. Despite the unfavorable political landscape, Barrow has made the race competitive. He has far outpaced his Republican opponent, state Rep. Lee Anderson, in fundraising. He also has been in general election mode from the start compared with Anderson, who emerged weakened from a competitive primary.

Illinois 2: Rep. Jesse Jackson Jr. (D) vs. Brian Woodworth (R)

Rep. Jesse Jackson Jr.'s biggest obstacle to a ninth full term in Congress might be himself. Jackson has been on medical leave since June for an undisclosed ailment, which his office later described as a "mood disorder."

In August, Rep. Patrick Kennedy told CNN that his longtime friend and colleague was suffering from "serious depression -- deep, deep depression."

In mid-October, CNN confirmed that Jackson was the subject of a federal investigation over possible financial improprieties. In late October, Jackson released a campaign robocall to constituents saying he was undergoing treatment for "several serious health issues" and asked for "your continued patience as I work to get my health back."

Republican opponent Brian Woodworth, an attorney and university professor, has criticized him for leaving the district unrepresented. Despite his absence, Jackson is expected to win.

Illinois 8: Rep. Joe Walsh (R) vs. Tammy Duckworth (D)

Freshman Republican Joe Walsh is high on the list of most-endangered GOP incumbents. Walsh barely won his seat in 2010 and redistricting has made it more Democratic. He has the additional misfortune of running in a presidential election year when favorite son Barack Obama is heading the ticket for the other party. Walsh has made headlines with a number of controversial statements, including his assertion that medical science has advanced to the point where abortions are never necessary to save a woman's life. Democrat Tammy Duckworth, a decorated Iraq war veteran, led in fundraising and entered the final stretch with an advantage.

Illinois 10: Rep. Robert Dold (R) vs. Brad Schneider (D)

Republican Robert Dold won this Democrat-friendly district in the Republican wave of 2010, replacing fellow Republican Mark Kirk, who ran for the U.S. Senate. The redrawn district is more Democratic-friendly, but Dold has kept the race competitive. His Democratic opponent is businessman Brad Schneider, who emerged battered from a competitive primary. Dold entered the final month of the campaign with a huge cash advantage but Schneider has benefited from sizable TV ad buys from the national Democratic Party and from a pro-Democratic super PAC, but he was trailing the overall TV ad dollars invested by Dold, the national Republican Party and the U.S. Chamber of Commerce.

Iowa 3: Rep. Tom Latham (R) vs. Rep. Leonard Boswell (D)

Merged district

Iowa was one of 10 states to lose seats in Congress because of redistricting, setting up a member-on-member showdown between two veteran lawmakers in a merged Des Moines-area district. Democrat Leonard Boswell represented much of this new district in the late 1990s. Republican Tom Latham has a fundraising advantage due in part to his friendship with Boehner. The cash advantage is apparent on the airwaves, where Latham has outspent Boswell, even when counting the considerable assistance the Democrat received from his national party. Boswell is no stranger to tight races. He survived the Republican wave of 2010. The presidential race will boost Democratic turnout, but his new district has many more "red" counties than the one he represented for 10 years. The race will be competitive.

Iowa 4: Rep. Steve King (R) vs. Christie Vilsack (D)

Republican incumbent Steve King's bid for a sixth term in Congress has been his toughest. King won re-election in his old western Iowa district with 66% of the vote in 2010, and he 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 comprises mostly counties won in 2008 by John McCain. King has had a fundraising advantage over Vilsack. But Vilsack is the strongest candidate Democrats could have fielded. She has been competitive financially. The political makeup of the district is still 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 officer and tea party favorite. Boustany represents more of the new district than does 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)

Republican Roscoe Bartlett's bid for an 11th term appears to be his last. The long-time western Maryland representative was a 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 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 off 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 off 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)