5. The field
While Rubio has led in all early polls of the potential 2016 field, there are a number of other strong candidates considering bids, many of whom took a pass on running in 2012. While that might not be a deterrent, it’s highly unlikely he’d be able to cruise to the nomination.
An even bigger question is whether Hillary Clinton runs. Clinton could clear the Democratic field and while her astronomical current standing in the polls is likely to come down, she presents a formidable obstacle, especially for a candidate like Rubio who is young enough to wait for another opportunity.
Clinton led Rubio in a recent national poll from Democratic-affiliated Public Policy Polling (PPP) by a large 49 to 41 percent, and has led in PPP polls over Rubio in such red states as Texas and Kentucky. He’s a very popular politician, but it may be smart not to take her on if she remains anywhere near as popular in a few years as she is currently.