A few names that come to mind: Scott Brown, Tim Pawlenty, Jon Huntsman, Rick Perry or one of his former primary opponents.
Let us take a look at some names that have been tossed around already:
Michelle Bachmann: Unfortunately, the American voter base still reeks of sexism, so she could cost Romney the election. A lot of people said that's what happened in 2008 with John McCain and Sarah Palin.
Jeb Bush: His last name is Bush, enough said.
Chris Christie: It's very likely that he does not want to do anymore than he is doing now. Possible health concerns.
Donald Trump: I doubt he would want to take a pay cut.
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Who knows what evil lurks in the hearts of men?