I am convinced that he is intentionally trying to stick it to the Republican party. They all abandoned him after this story broke. They didn't abandon Vitter. Yeah Craig pled guilty, but this really had to do with the fact that it was gay sex and that would hurt their image. He's probably annoyed by that, considering that he's probably conflicted about his sexuality to begin with. So he probably just figures if they're going to screw him over, he might as wellstay in the Senate for as long as he can, he has nothing to lose.
I wouldn't doubt this.