Hi Frank. Well, I think your question shows part of the problem here. You already assume that Obama is 'rational' simply because he looks and sounds it in comparison to Bush (and a whole lot of other recent US presidents). But that does not mean he is exempt from the run-of-the-mill delusions that plague American politics. Principal among these is that the US really is some fantastic military power and can do whatever it wants militarily.
But I do not want to enter into a discussion of what 'rationality' might mean in a US political context. For what it's worth, I think nearly all US mainstream political leaders are insane (as in disconnected from reality, unable to understand reality's limits). Below, Jake mentions Putin. The difference between Obama and Putin is that Putin is probably already an order of magnitude more realistic simply by virtue of not being an American.
The real point is what Obama has said about Afghanistan. Basically, he said 'Screw Iraq, Afghanistan's the good war and that's where we're going!' Now I do not think this is at all able to square with some sort of strategic withdrawal. If the populist angle mattered at all (which it doesn't), Obama would have said, 'I know you're all sick of bullshit wars, so I'm bringing our troops home, especially from Afghanistan, which is strategically pointless.' And with as little faith as I have in Americans, I think that would have gone over a treat. But that isn't what he said at all. He is on record as saying he will increase the US military commitment to Afghanistan.
We all know that politicians lie to get elected, but the lies are usually positive ones. They don't usually promise to keep fighting a stupid, immoral, unwinnable war that is unpopular domestically, unless they are actually dumb enough to mean it. And I submit that Obama, despite how suave he appears, is dumb enough.
If Obama told any lies to get himself elected, they were the 'hope and change' ones, not the 'We're staying in Afghanistan' ones.