A piece of history that's working against Joe Sestak on Tuesday is that, true to the pattern for the past 60 years Pennsylvania will be electing a Republican governor.
For the past 60 years, the voters in Pennsylvania have changed the party in the governor's mansion every eight years, like clockwork. Ed Rendell, a Democrat, has served his eight years, so it's time to elect a Republican governor, and that would be Tom Corbett.
And vote-splitting takes extra effort, so a voter who votes for a Republican governor is more likely to vote for a Republican senator.
Sestak could still be elected to the Senate even if Tom Corbett is elected governor, but it will be a little bit harder, and in a close election that little extra edge could make a difference.