3. Sen. Dick Lugar, R-Ind.: Lugar completes the trio of Republican senators who came out of the 2010 cycle expecting a tea party challenge -- and again, he has fared somewhat better than he could have. Lugar did get an early tea party challenger in Indiana state Treasurer Richard Mourdock, but Mourdock doesn't seem to be getting the momentum necessary to knock off the longtime senator.
He lags in fundraising, and despite efforts to consolidate tea party support behind him, it now looks as though Republican auto dealer Bob Thomas will enter the race after the start of the new year - a development that would potentially serve to divide the anti-Lugar vote
2. Sen. Bob Casey, D-Pa.: 2010 was a big year for Republicans in Pennsylvania -- they won Senate and gubernatorial races in the state -- and it looks like the Keystone State could be a presidential battleground in 2012. Casey could potentially be vulnerable, but so far the GOP field is big and muddled, with no obvious frontrunner.
1. Sen. Joe Manchin, D-W.Va.: Manchin won a hard-fought race in the 2010 special election for the late Sen. Robert Byrd's, D-W.Va., seat, and there was no reason to believe 2012 would be any easier for him - especially in a presidential election year in a state where President Obama is extremely unpopular.
But Manchin has no Republican challenger so far, and Rep. Shelley Moore Capito, the more popular Republican in the state, has given no indication of interest in a bid. And Manchin's own high popularity makes a run against him unappealing. A candidate could still emerge - perhaps another self-funder like his 2010 opponent, John Raese - but for now, it's looking like Manchin lucked out.