Elizabeth Warren

But politicians have a long history of ignoring their previous denials when circumstances change. Barack Obama frequently dismissed the notion that he'd seek the presidency so early in his career, only to ditch those denials and announce a campaign in 2007. It's unlikely that Warren would challenge Clinton should Clinton, as expected, run in 2016. The Massachusetts politician joined her fellow female senators in signing a letter urging Clinton to run for president again. But, should she pass on another bid, Warren could always change her tune.