I try to avoid simply repeating things that other people blog, but this excerpt of President Obama's news conference from December, via Mike Konczal, is pretty incredible:

THE PRESIDENT: …Marc Ambinder.
Q Mr. President, thank you. How do these negotiations affect negotiations or talks with Republicans about raising the debt limit? Because it would seem that they have a significant amount of leverage over the White House now, going in. Was there ever any attempt by the White House to include raising the debt limit as a part of this package?
THE PRESIDENT: When you say it would seem they’ll have a significant amount of leverage over the White House, what do you mean?
Q Just in the sense that they’ll say essentially we’re not going to raise the — we’re not going to agree to it unless the White House is able to or willing to agree to significant spending cuts across the board that probably go deeper and further than what you’re willing to do. I mean, what leverage would you have –
THE PRESIDENT: Look, here’s my expectation — and I’ll take John Boehner at his word — that nobody, Democrat or Republican, is willing to see the full faith and credit of the United States government collapse, that that would not be a good thing to happen. And so I think that there will be significant discussions about the debt limit vote. That’s something that nobody ever likes to vote on. But once John Boehner is sworn in as Speaker, then he’s going to have responsibilities to govern. You can’t just stand on the sidelines and be a bomb thrower.
And so my expectation is, is that we will have tough negotiations around the budget, but that ultimately we can arrive at a position that is keeping the government open, keeping Social Security checks going out, keeping veterans services being provided, but at the same time is prudent when it comes to taxpayer dollars. A shockingly poor calculation.

Now, in the administration's defense, no Congressional party had ever previously used the debt ceiling to jack up the president for substantive concessions. Still, it was clear that the time that Republicans were committed to pushing the boundaries of their formal powers as far as they would go, and Obama utterly failed to anticipate this. Obama could easily have thrown in an agreement to raise the debt ceiling as part of a deal to implement Republican-demanded proposals to increase the deficit. But the Democrats seemed to think the debt ceiling would make the Republicans more responsible and bipartisan.