Democrats will keep control of the Senate next year, holding on to enough shaky seats while picking up three seats now occupied by Republicans.
Democrats also picked up seats in Indiana and in Maine.
In a mild surprise, Rep. Joe Donnelly, D-Ind., beat Republican Richard Mourdock, who ousted longtime Sen. Dick Lugar in Indiana's GOP primary.
In Maine, independent candidate Angus King, who is expected to caucus with the Democrats, won the seat now held by retiring Sen. Olympia Snowe.
Wisconsin's U.S. Rep. Tammy Baldwin claimed victory after posting a 50.7-46.6 percent lead over former Wisconsin Gov. Tommy Thompson with 84 percent of the vote counted. Baldwin became not only the first female U.S. senator from Wisconsin but also the Senate's first openly gay member.
In the battle of former governors in Virginia, Democrat Tim Kaine defeated George Allen to keep retiring Sen. Jim Webb's seat blue.
In Connecticut, Democratic Rep. Chris Murphy defeated Republican Linda McMahon, who also lost her 2010 senatorial bid, to succeed Sen. Joe Lieberman, an independent who caucuses with Democrats.
In the House, Rep. Paul Ryan lost his bid to be the vice president but will remain one of Wisconsin's congressional representatives, NBC said.
In Minnesota, two Republican House members were having trouble winning another term. Onetime GOP presidential candidate and Tea Party stalwart Michele Bachmann was clinging to her District 6 seat to Democratic challenger Jim Graves by a 341-vote margin with 68 percent of the votes counted. In the 8th District, Rep. Chip Cravaack, who upset longtime Democratic Rep. Jim Oberstar two years ago, was trailing Democrat Rick Nolan, a former congressman, 48.7 percent to 51 percent with 32 percent of the precincts counted.
In the redrawn 8th District in Illinois, Democrat Tammy Duckworth, a disabled Iraq War veteran, was pushing hard against Tea Party Republican freshman Rep. Joe Walsh.
In Georgia, all 13 House incumbents won, including Republican Doug Collins, who took the one open seat, leaving the delegation tied 7-7.
In Florida's 18th District, Rep. Allen West, a conservative black Republican and Tea Party favorite, was in a close and expensive battle with challenger Patrick Murphy, The Palm Beach Post reported. Campaign spending in the race had reached $23 million.