Something financial or sexual in his past has given someone leverage. Other than that "foam party" possibility, I don't know enough about his background to pick which one he is vulnerable to.
In a way, Marco Suave was a Republican "Obama" in that when he arrived on the scene, he was obviously propelled there by something other than hard work. Rush's praise for the guy seemed like the GOP had their hand up Rush's bum too.
I think most everyone was smitten with Little Marco when he first arrived on the scene. My, my, how things have changed...