I'd only mention that whereas Drum puts the blame for liberal disappointment on the Democratic Party, not Obama, I'd push a bit harder on that. Suppose you're a liberal and live in, oh, Henry Waxman's district. Your Member of the House, both your Senators, and your president all did what you wanted; they couldn't do more not because of the Democratic Party per se, but because of Ben Nelson, and Evan Bayh, and Joe Lieberman, and a handful of others in the House and Senate.
Moreover, those Democrats didn't do what you wanted, in many cases, because they honestly disagreed with what you want. And, in many cases (not Connecticut, of course), that's because politicians with your views would be hard to elect in those places.
In other words, it's not the president's fault, or the party's fault, or the structure of the government's fault: it's the reality of living in a democracy with 300 million other people.
Still, I weep not for Blanche Lincoln, and I will weep not for Ben Nelson.