That's the purist progressive argument, because he hasn't been progressive enough. Frankly, I never expected him to be that progressive, even if that was what he truly wanted to be. Our system of government is designed to frustrate making major changes quickly, and to empower the opposition.
When you take into account what he has done, and the prospect of reinforcements in 2012, I don't think he should be dumped. I think we should have his back.
Footnote to the author of the article in the first link: 1968 didn't exactly restore democracy. It gave us Nixon, who gave us Watergate, which almost cost us our democracy. Something to think about when you want to have a temper tantrum.