If Bush can’t turn his advantages into broader GOP support by the end of the year, you can expect establishment and rank-and-file Republicans alike to start scrambling for alternatives. This is exactly what happened in late 2011 – while Mitt Romney ultimately won, his sagging numbers prompted Texas Gov. Rick Perry to enter the race and GOP donors to consider drafting New Jersey Gov. Chris Christie into an emergency run. 

Of all the candidates, Rubio may strike the next best balance between a conservative base demanding one of their own and big donors who want to win without rocking the party boat too hard. Rubio is polished, and at 43 years old he presents a youthful contrast to Clinton and Bush. Rubio’s a passionate hawk whose views on national security won’t set off alarm bells in establishment circles if he gets close to the nomination. That trait could be especially crucial against likely rivals Sens. Rand Paul and Ted Cruz, whose more unconventional views make some in the party nervous, and against Wisconsin Gov. Scott Walker, who is surging in polls but still new to the foreign policy arena.

The potential is all there – if only he can get past immigration.