One of the night's half-dozen or so competitive Senate races was the contest between Claire McCaskill and Todd Akin in Missouri. McCaskill had come into office during the wave election of 2006, when many Democrats were voted into office as a reaction against the unpopular Bush administration. However, since that time, Missouri's politics relative to the rest of the nation's had become more conservative. While Barack Obama had come within a fraction of a percentage point of winning Missouri in 2008, it wasn't even on his slate of states to contest in 2012.
For a long time, it looked like McCaskill would fall, a victim of her state's conservative shift. Her challenger, Representative Todd Akin, was doing well in polls against her.
He then made a statement about abortion and rape, saying that "legitimate rape" rarely leads to pregnancy. This statement was widely judged to be untrue and tasteless, and members of Akin's own party told him to withdraw. He did not, but he quickly fell behind McCaskill in polling. The polling seems to be accurate, because with almost all of the vote counted, McCaskill leads Akin 55-39.
Although I don't know if it is true, I suspect that Akin's statements might have reverberated beyond his race and cost other Republicans their jobs. For example, in the Massachusetts contest, Scott Brown, a moderate Republican might have been acceptable to the voters in Massachusetts. But as the Republican Party became to be identified in people's minds with statements such as Akin's, it might have alienated voters. This is speculation, but it is one possible reason for tonight's results.