The reasoning's simple: Greenwald's part of the left, just like Obama and the Democrats who controlled the House and had a filibuster-proof majority in the Senate for a while. Greenwald's side failed to pass enough progressive legislation, therefore Greenwald's primarily responsible.
If you don't like this reasoning, complain to Greenwald: he used the same reasoning to say voters will determine that Republicans are not primarily responsible for the failure to pass progressive legislation, laying responsibility instead at Obama's feet, especially with repeated reference to the 60-person Senate majority. Greenwald does some really good work on civil liberties but mixes it in with this terrible reasoning. Fault lies primarily with the Republicans, secondarily with the Democratic Senators (and some Representatives) who refuse to vote in defense of the middle class and for scientific reality. Obama is not a Prime Minister. Maybe somewhere Greenwald has laid out how he thinks Obama could've pushed legislation through, but he certainly didn't make that point when I listened to him.
That's not to say Obama is blameless - Greenwald rightly points to the HAMP mortgage modification failure as a self-inflicted wound. On legislation though, he and we have to deal in reality.
Speaking of reality and legislation, we might want to look ahead. A best-case scenario in 2012 elections will bring Obama back along with marginal control of the Senate and House. I'm guessing more likely that Obama returns and we only get one of the two congressional houses, and even worse scenarios are very plausible. The best case scenario, in other words, still has us in worse position than 2009-2010. Things generally get worse in mid-term elections for the majority party, and the majority party starts getting tired and often corrupt after many years in office.
I think the best chance to pass climate legislation for another four years was the one that we had before the 2010 elections. It really is a shame that many enviros failed to push for cap-and-trade, because as marginally, politically viable as it was, it was the best shot for years to come. A national carbon tax was not politically meaningful and will take a lot more changes of political fundamentals before it will be. Some enviros missed the boat last time. We can still work together though do things on a piecemeal basis and at the state and local level instead, and gradually enforce carbon regulation through the Clean Air Act and other laws.