Assuming that Hillary Clinton can't lead the Democratic Party and the rest of the country into Bizarro World, there's a good chance that Barack Obama will be the next President of the United States. By my reckoning, that would make him only the fourth cool President in our history.
A genuinely cool President has to be someone who would be cool even if he or she wasn't President, someone you'd think it would be cool to hang out with in a situation that had nothing to do with politics. That leaves us with Thomas Jefferson, Theodore Roosevelt and John Kennedy. Kennedy makes the list by the skin of his teeth, since it would only be cool to hang out with him somewhere like Las Vegas or Hollywood, and only if you were in serious party mode and relatively drunk. You'd have to be able to forget that he was a married man with two small children. (Bill Clinton was cool in a similar sort of way, but only if you grew up on a farm and met him on a rare visit to a roadhouse on a rocking Saturday night.)
Jefferson and Kennedy were sexual creeps, so Obama would be only the second cool President who was also a decent human being in his private life.
How cool is that?