If Santorum had any vision for a post Senate career in politics, maybe he should have done a "Romney" and chose not to seek re-election. Unlike Romney, Santorum was elected twice, so it could be spun into support for term-limits or some other positive.
Still, just like most members of Congress, Santorum felt the need to run again possibly just for running's sake.
He thinks he can win and he still can. I had wondered if he would pull a Romney to run for President but he's still young. He doesn't need to quit to pursue other office. In fact, he could come back in 2010 for either the Senate seat or the Governorship if Swann loses this year.
