Democrats, bolstered by polling that shows that many voters blame the tea party for gridlock in Washington, had tried to try to pin the label on virtually every Republican incumbent and challenger.

The "Tea Party Republican Congress has a 13% approval rating," House Democrats' campaign chief Rep. Steve Israel of New York told reporters last month. He said Democrats had a chance to regain the majority because "there is a deep sense of buyer's remorse spreading throughout this country."

With the bulk of this cycle's competitive races concentrated in districts represented by more moderate members of each party, the outcome of this election could mean an even more polarized House in 2013.

The GOP conference could include more conservatives and fewer moderate Democrats, whose ranks were decimated in 2010. That could tilt the Democratic caucus leftward.

A recent study by the Cook Political Report found that the number of swing districts in the nation dropped from 164 to 99 over the past 14 years. That decline has widened the ideological divide between the two parties.

"There's a remarkable reduction in the number of members who have an incentive to compromise," Wasserman told CNN.

Key House race snapshots

Arizona 1: Jonathan Paton (R) vs. Former Rep. Ann Kirkpatrick (D)

Open Republican-held seat

This redrawn district covers most of northern and eastern Arizona. The Democratic nominee was Ann Kirkpatrick, who was elected in 2008 and was swept out in the Republican wave two years later. The Republican nominee was Jonathan Paton, a former state senator. Kirkpatrick had a sizable fundraising advantage over Paton, but national Republicans invested heavily to help close the gap in TV ads. This seat was a top priority for both parties.

Arizona 2: Rep. Ron Barber (D) vs. Martha McSally (R)

Democrat Gabrielle Giffords would have run here had she sought a fourth term. Giffords is recovering after being shot in January 2011 in Arizona. Her district director Ron Barber, who was also wounded, won a special election to fill her seat when she resigned last January. His opponent was Republican Martha McSally, a retired Air Force colonel and combat pilot. Barber had a financial advantage at the start of October though McSally remained competitive on the airwaves. Still, Barber was expected to win.

Arizona 9: Kyrsten Sinema (D) vs. Vernon Parker (R)

New district

The battle for this new district pitted Democrat Kyrsten Sinema, a former state senator, against Republican Vernon Parker, the former mayor of Paradise Valley. Both parties invested heavily in the race, though a Democratic super PAC tipped the TV ad war balance of power slightly in the Democrat's favor.

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.