Why Did Senate Democrats Defy Obama

So, Senate Democrats have done the unthinkable: They've defied Barack Obama, and denied funding for his efforts to close Club Gitmo. So, for the moment, I must commend the Senate Democrats! Bravo! (Of course, I realize that the lack of funding is only temporary -- the Dems merely want detailed plans for closing Gitmo.)

However, a thought occurs to me: With Obamas "soaring" approval rating, why would the Senats Democrats defy the President like this? There has to be a reason for it. Really, this is the first (and only) issue that they have broken with the President. They've been in lockstep on the numerous bailouts, ballooning spending, and now on his efforts to take over the health care system. Why suddenly break on such a specific issue?

I have a theory: I think the Senate Democrats were acting with Obama's blessing, and at his request. Obama has finally figured out that it's not feasible to close Gitmo. Nobody will take the detainees. We don't want them in American prisons. And he simply doesn't know what to do with these guys. Yet, Obama can't break a campaign promise, even though the media would certainly let him get away with it. So, he needs someone to take the fall -- If the Senate blocks funding. then he can't keep his promise and he still hasn't broken it.

What do you think? Is there a better explanation?