John Mearsheimer was very direct and deeply pessimistic. Ten years ago, I doubt I would have believed that Mearsheimer's critique of US foreign policy would essentially mirror a standard leftist perspective. There are differences, of course, but on Iraq Mearsheimer is making an argument that would fit very comfortably into the netroots. Mearsheimer argued that Iraq has been and will continue to be a disaster, but that because of domestic politics and institutional dynamics we'll still be there in five years and beyond. The stab-in-the-back narrative that's being prepared by the Republican Party will succeed in scaring a Democratic president and Democratic congress from taking any decisive steps to end the war. At the same time, the senior theater leadership in the armed forces are committed to not losing, due to their perception of the institutional disaster that resulted from the Vietnam War.
That's too pessimistic by half. Although it is true that the Democratic leadership begs to be underestimated, Mearsheimer still underestimates them. When Reid and Pelosi caved into Bush last spring, they didn't fall apart just because the Republicans generated a "stab in the back" narrative. They caved because they were afraid of the power of the "stab in the back narrative" in the context of a constitutional showdown between themselves and President Bush over setting a deadline for withdrawal. Specifically, they were afraid that their own caucuses wouldn't back them in such a showdown.
The situation will be very different if a Barack or Hillary administration is working with a Democratic Congress in 2009. Given that there's a consensus among Democratic heavyweights to either reduce American troop levels to 70,000 or redeploy to Kuwait, there will be no constitutional crisis over passing any of the needed legislation. The right-wing attack media and the military in Iraq might object, but there is no reason to think that the right will be able to set the agenda after the Republicans lose the presidency and lose more ground in Congress in 2008.
Mearsheimer is pessimistic because Hillary, Obama, Reid, and Pelosi are all relatively cautious leaders who try to avoid big stakes confrontations.
But withdrawal from Iraq is not going to require a huge confrontation. Consequently, the Democrats are a good bet to get it done when they take over in 2009.