In California, three Republican incumbents were trailing to Democrats -- Dan Lungren to Ami Bera 88,406 to 88,222, Brian Bilbray to Scott Peters 105,646 to 104,832 and Mary Bono Mack to Raul Ruiz 83,402 to 78,845, CNN reported.
News outlets, including the San Francisco Chronicle, projected Ruiz the victor, but Mack was refusing to concede because of an undetermined number of uncounted absentee and provisional ballots, the Los Angeles Times reported.
Allen West, one of two black Republicans in Congress, was behind Democrat Patrick Murphy 160,328 to 157,872 in a South Florida district, CNN said. West, first elected in 2010 and a favorite of the Tea Party, was refusing to concede on the grounds that some provisional votes remained to be counted, The Palm Beach Post reported.
Hearings were scheduled for Thursday and Friday on motions filed by an attorney for West to impound ballots and voting equipment for a potential recount in St. Lucie and Palm Beach counties.
Outcomes were up in the air in two Arizona districts. Democratic incumbent Ron Barber, who replaced Gabrielle Giffords in a special election, lagged his Republican challenger, Martha McSally, 114,079 to 113,653. Democrat Kyrsten Sinema was ahead of Republican Vernon Parker 80,769 to 78,054 in a newly created Phoenix-area 9th District, CNN said.
In North Carolina, Democratic incumbent Mike McIntyre led Republican challenger David Rouzer 167,590 to 167,057.
In Louisiana, which lost a congressional seat on the basis of population, two Republican congressmen, Charles Boustany and Jeff Landry, will square off against each other in a runoff in the redrawn 3rd District where no candidate received a majority.
Boustany, with 139,113 votes (44.7 percent) and Landry with 93,524 votes (30 percent) were the top two vote-getters, The (Baton Rouge) Advocate reported.
The runoff will be Dec. 8.
Republicans retained control of the House, although their majority was cut in Tuesday's election.
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