A few points here. One, Obama was backed in 2008 by everyone to the right of Dennis Kucinich and to the left of Colin Powell, nearly all of them believing that Obama stood for what they believed in. Someone in that coalition just had to end up disappointed.
Second, this article reveals an important point about partisanship: everyone hates it until they think their side is losing, and then they want more of it. That is, "I want an end to the bickering and I want politicians to set aside petty grievances and do what's right, but they damn well better fight for the things I believe in and not sell out to people I perceive as wrong or evil."
I disagree with Smith that next year's election will help settle this internal debate. If Obama loses, many on the right will say it was because he was too far to the left, and many on the left will say it's because he gave too much to the right. That is, he was both too partisan and not partisan enough. If he wins, that will be either evidence of the genius of his post-partisan style or of his tenacious defense of liberal values. It's all relative.