Greenwald, Chait, and Jonathan Bernstein are in the middle of a three-way cage-match over the question. Chait calls Greenwald "a fanatic" for letting his "sense of betrayal in issue areas where Obama wields tremendous influence to bleed over into issue areas where he does not." Here's the end of Greenwald's response to Chait:
As I've acknowledged from the start, the President does have some constraints in the area of domestic policy and will not always be able to move Congress to do what he wants. The complaint has been not that Obama is omnipotent and thus failed to get good progressive bills, but that he did not use his substantial leverage to try (again, just contrast what the White House did on the war supplemental bill). But the claim that he has virtually no leverage to influence what Congress does on domestic policy is silly, and to see how true that is, just look at the central role the White House played in killing the public option and -- according to its own Treasury official -- is now playing by dictating which progressive provisions will be killed from the financial reform bill and which ones will remain.
Bernstein reiterates his argument, which is more modest than Greenwald makes it out to be.