I'd put Obama in Ravenclaw too: he's not only very bright, but also very obvious about it, despite the fact that it clearly alienates some people.

I also tend to associate idealism with Ravenclaw, simply because there's no where else it would fit. The Slytherins would have no interest, and the Hufflepuffs seem too feet-on-the-ground to go in for that. The Gryffindors might go in for it, but Hermione seems to be the only one who does, and everyone else thinks it's a bit ridiculous really.

You could also make an argument for Slytherin, perhaps, but I think that's an easy argument to make for really any of the modern presidents. You just don't end up in high office without a burning flame of ambition these days. But the game's no fun if everyone's a Slytherin, you know?