The Florida Senate race
The stage seems set for another NY-23-style debacle. Florida is the purplest of states, often splitting its vote almost exactly 50-50 (most notoriously in the 2000 Presidential election), not very hospitable turf for too-red or too-blue candidates. As a centrist, Crist would likely have won; he still has a good chance of winning as an independent. If he does, his bridges with the Republican party will have been well-burned. Even if he doesn't, he could split the Republican vote and help the Democrat, Kendrick Meek, to win. Either way the Republicans are now at real risk of failing to capture a Senate seat which, by sticking with Crist, they would likely have gained.