But, this seat will only flip anyways, should Rubio run for president. Which he will decide any day now.
Even if Rubio announces tomorrow that he's running for president rather than Senate, there's still the chance that he flames out early, a la Pawlenty, and then six months from now, after having dropped out of the presidential race, he gets "drafted" to run for reelection for his Senate seat instead.
Though crawling back with his tail between his legs after an aborted presidential run would likely hurt him.