As much as I hate to defend Lindsey Graham, I honestly think he's running for the VP slot. He would make an appealing VP for the Republican base -- hawkish on defense and a veteran of senate dealmaking.
The only reason why I chose Lindsey Graham for my example, was that he's stuck in JV debates, and had I could articulate a reason for his candidacy -- as opposed to Bobby Jindal, Rick Santorum, or George Pataki. I honestly can't figure out why their staying the race, except for perhaps for personal marketing reasons.