Sargent puts the tax fight in perspective:
Obama's argument with the left, at bottom, is more a dispute over what's achievable, and less an argument over what is desirable to achieve. Obama opposes extending the high end tax cuts, just as the left does. His disagreement with the left is over whether there's another way to achieve the goals Obama and the left agree on: Extending the middle class cuts and extending unemployment benefits. The left says a protracted fight would achieve those things. Obama and his advisers say a fight wouldn't achieve those things, or at least that a fight wouldn't achieve them in time to stave off a tax hike for the middle class. Hence his willingness to reach a deal.
Indeed, Obama's outburst yesterday was rooted in genuine frustration with the left for not agreeing with him about what's possible given today's political realities.