- Democrats could hit 200 House seats, if they hold leads in undecided races
- Redistricting nationwide turned solid seats into hotly contested races
- Handful of outstanding races could be decided by fewer than 700 votes each
- Potential upsets include Tea Party favorite Allen West and seven-term Republican Mary Bono Mack
Seven of eight unresolved U.S. House races remain too close to call with votes still being counted and potential losers preparing and, in some cases, already launching court challenges.
Republicans maintained control of the House in Tuesday's election, but Democratic gains could give them 200 seats in the 435-seat chamber.
Fewer than 700 votes represented the margin of difference in a handful of the House races still outstanding on Thursday.
Democratic incumbent Mike McIntyre held a lead of 533 votes over Republican challenger David Rouzer in the race for the North Carolina's 7th Congressional District seat.
Republican incumbent Brian Bilbray trailed Democratic Port Commissioner Scott Peters by 658 votes in their fight for California's 52nd District seat.
Republican Martha McSally led by 533 votes over Arizona Rep. Ron Barber in the contest for Arizona's 2nd District.
After provisional and absentee ballots are counted, the race for California's 7th Congressional District could prove to be the tightest in the country. Republican incumbent Rep. Dan Lungren trailed Democratic challenger Ami Bera by 184 votes.
The remaining four seats up for grabs -- Arizona's 2nd and 9th, Florida's 18th and California's 36th -- could be decided by fewer than 5,000 votes.
A runoff will take place in Louisiana's 3rd District after none of the five candidates took the required 50% of the vote to claim victory.
Two current Republican congressmen, Charles Boustany and Jeff Landry, found themselves in a battle for the seat after the state lost a House seat because of its lower population after the 2010 Census. Boustany beat Landry in Tuesday's election by 15 points - 45% to 30%.
In two high-profile potential upsets, Florida's Rep. Allen West and California's Rep. Mary Bono Mack, both Republicans incumbents, refused to concede.
West rode the tea party wave to office in Florida's 18th Congressional District during the 2010 midterm elections, unseating three-term Democrat Rep. Ron Klein by more than eight points.
This time around, West faced a tough opponent in Republican-turned-Democrat Patrick Murphy.
The contest between the two is expected to be one of the most expensive races in history. West raised significantly more than Murphy -- $17 million vs. $3.6 million.
But refusing to accept defeat after a vote count showed him down by 2,500 votes, West is demanding a full recount.
"There were numerous other disturbing irregularities reported at polls across St. Lucie County, including the doors to polling places being locked when the polls closed, in direct violation of Florida law, thereby preventing the public from witnessing the procedures used to tabulate results," a statement released by the West campaign said.
The West campaign filed injunctions against the supervisors of elections in Palm Beach County and St. Lucie County to impound voting machines and paper ballots.
"We will continue to fight to ensure every vote is counted properly and fairly, and accordingly will pursue all legal means necessary," the statement concluded.
The fiery tea partier isn't guaranteed a recount under Florida election law which only stipulates an automatic recount in races if the margin of difference between the candidates is a half-percent or less. As close as the race is, it doesn't meet that criterion.
Bono Mack similarly refused to concede.
"With more than 180,000 ballots still to be counted around Riverside County, it is premature to consider any election results final," Marc Troast, the congresswoman's political director told the L.A. Times. "Congresswoman Mary Bono Mack and her campaign will be awaiting the impact of this large number of remaining ballots before making any further statements on the 36th Congressional District race."
The widow of former Rep. Sonny Bono and current wife of former Rep. Connie Mack IV -- who lost his bid for a Senate seat against incumbent Bill Nelson in Florida -- is down by about 4,500 votes. That total leaves her behind Democratic challenger Raul Ruiz 51% to 49%.
Lungren and Bilbray also have not conceded with provisional and absentee ballots still being recounted.
Bilbray's spokesman Patrick Howell said the race was "far from over," as additional ballots are processed.
The Registrar of Voters in San Diego County is in the process of counting approximately 475,000 absentee and provisional ballots which could determine Bilbray's race. Votes cast in San Diego county are cast in one of five congressional districts.
Lungren's race could drag on for weeks as Sacramento County election officials count the 162,000 vote by mail and 31,000 provisional ballots still outstanding. The 193,000 votes being counted in Sacramento County were cast in one of four congressional districts.
County election officials in California must submit final official results to the Secretary of State by December 7.
California has been an uphill battle for Republicans after redistricting moved reliably Republican seats like Bono Mack's into more Democratic territory.
Two races in Arizona also also remain uncalled.
The contest for former Rep. Gabrielle Giffords' seat between Barber and McSally finds Barber behind by 426 votes. Barber, former district director for Giffords, replaced her in a special election held after she was shot in the head and severely wounded in 2011.
The man convicted in the attack outside a supermarket that killed six people received a life prison sentence on Thursday.
And in a district across the state, Democrat Kyrsten Sinema is holding onto an almost 3,000-vote lead over Republican Vernon Parker while provisional and absentee votes are counted.
Parker might have Libertarian candidate Powell Gammill to blame if he does not win. Gammill won more than 6% of the vote in Tuesday's election despite urging supporters to stay home rather than vote on Election Day in protest of the political system.
The unresolved contest in North Carolina could be the second tightest 2012 congressional race after provisional and absentee ballots are counted for the district that encompasses Wilmington and northwest to the Raleigh suburbs.
Democratic Rep. Mike McIntyre faced a tough re-election challenge in a district that added Johnston County to McIntyre's and his hometown of Lumberton was cut from the 7th District this year after his seat, too, was redistricted.
Once the ballots are counted, either McIntyre or his Republican challenger and two-term state Sen. David Rouzer can request a recount if the margin remains a 1% or less. Both candidates have until November 20 to request a recount.
Gary Bartlett, the executive director for the State Board of Elections in North Carolina, said officials should know if Rouzer intends to request a recount before the November 20 deadline.