The idea is two fold. First, as Chris Dodd pointed out at the Drexel Debate, like it or not Clinton would have a harder time winning a general election due to excessive right-wing animosity. However, Obama went to to look past the election. He correctly perceives that with Democratic majorities in the house and senate in 2008, there is an opportunity to actually affect real, meaningful, progressive change in several key areas. Obama correctly, in my view, pointed out that he is in perhaps the best position to bring about big change, something that you can't do with a 50%+1 majority.

Clinton is attacking that problem by making her policy proposals more amneable to conservatives, but lets be honest; any serious attempt by a President Hillary Clinton to universalize healthcare, or tackle global warming, will be met with such conservative fury that even watering it down wouldn't salvage it. We would end up squandering opportunity with political mudfighting. This isn't Clinton's fault, but it's not something we should ignore either.

Obama is in a tough place. He's running the race he promised he would, and it's not resonating with a base that wants red-meat rhetoric and is yearning for partisanship. I trust that Obama has progressive roots, though, and I think that he's our best hope of actually achieving, post-election, transformational reforms.

It's a serious argument that I think is the strongest case for Obama.