California 30: Rep. Brad Sherman (D) vs. Rep. Howard Berman (D)

Merged district

One of the nastiest House races of 2012 was between two incumbent Democrats due to redistricting and the state's new primary system, in which the top two finishers advanced to the general election. Rep. Brad Sherman had at least one advantage over Rep. Howard Berman: He represented more of the redrawn Sherman Oaks-area district. Sherman won the primary with 42.4% of the vote compared with 32.4% for Berman. The remaining votes were split among five candidates. The race hit a nasty patch last month, when the two men shouted at each other at a public forum.

California 31: Rep. Gary Miller (R) vs. Bob Dutton (R)

Seven-term incumbent Rep. Gary Miller faced a tough challenge from a fellow Republican in a race also determined by California's new primary system. Miller's opponent is Bob Dutton, a state senator and businessman. Miller represented none of this redrawn district, while Dutton represented much of it in the state legislature.

California 36: Rep. Mary Bono Mack (R) vs. Raul Ruiz (D)

Rep. Mary Bono Mack, seeking an eighth full term in the House, was a frequent target of Democrats hoping to pick off a Republican in a Democratic district. This year, she found herself fending off a strong challenge from Democrat Raul Ruiz, a Mexican-American, Harvard-educated physician. But Bono Mack survived strong challenges before and has a moderate voting record. She also prevailed over Ruiz in her first one-on-one matchup, the June "top-two" primary in which they appeared together on the same ballot.

California 44: Rep. Laura Richardson (D) vs. Rep. Janice Hahn (D)

Merged district

Redistricting forced another pair of Democratic incumbents to face off this November. Rep. Janice Hahn won a July 2011 special election to replace retiring Democratic Rep. Jane Harman. Rep. Laura Richardson was elected in a 2007 special election to replace the late Juanita Millender-McDonald. Hahn appeared to have an advantage due, in part, to an ongoing ethics saga for Richardson that resulted in a reprimand and $10,000 fine by the House Ethics Committee for campaign finance violations involving her congressional staff. Hahn also enjoyed a huge fundraising and cash-on-hand advantage at the start of October. Hahn trounced Richardson in the primary.

Florida 9: Former Rep. Alan Grayson (D) vs. Todd Long (R)

New district

In just one term in Congress, Democrat Alan Grayson mastered the art of making headlines with his blunt and abrasive rhetorical style. During the debate over health care, he said the Republican health care plan was, "Don't get sick, and if you do get sick, die quickly." He also said on CNN that Republicans were "foot-dragging, knuckle-dragging Neanderthals." In a 2010 TV ad, he called his Republican opponent, Daniel Webster, "Taliban Dan." Although he quickly became a hero among liberals, Grayson went on to lose his bid for a second term by a staggering 18 points.

Grayson was running in a new district in the Orlando suburbs and his Republican opponent was Todd Long, an attorney, small businessman and conservative radio show host.

Florida 18: Rep. Allen West (R) vs. Patrick Murphy (D)

Rep. Allen West was a top target for Democrats The freshman Republican's sharp rhetoric during his first term did not endear him to colleagues across the aisle. For instance, West last summer e-mailed Democratic National Committee Chairman Rep. Debbie Wasserman Schultz that she was "the most vile, unprofessional and despicable member of the U.S. House of Representatives." West's Democratic opponent was Patrick Murphy, a businessman and executive with a construction firm.

Florida 26: Rep. David Rivera (R) vs. Joe Garcia (D)

The race in Florida's southernmost congressional district was a rematch of 2010, but the dynamics could not have been more different. Republican incumbent David Rivera was elected in the Republican wave two years ago. Democrat Joe Garcia, a former Miami-Dade County Democratic party chairman, lost by nine points. The key difference this time was that Rivera was dogged by scandal and ethics issues. The district is still Republican-friendly and Garcia entered the final stretch in better position than two years ago.

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

Moderate Georgia Democratic Rep. John Barrow was reelected to a fifth term in the House on Tuesday, and is the last white male Democrat from the Deep South in the House of Representatives, CNN projects. The remaining Democratic congressmen from Louisiana, Mississippi, Alabama, South Carolina and Georgia are African-Americans.