Bowers likes to make the point that the administration does more to lean on progressives than it does to lean on moderates. This, however, ignores the basic reality that the administration has more leverage over progressives than it does over moderates.I talked about this a bit yesterday in a different context yesterday, in response to Robert Reich's suggestion that Obama provide cover for marginal Congressional Democrats. As Yglesias implies, Obama just can't do that. People in Massachusetts might trust Obama if he says that John Kerry is a good guy; people in Montana are generally not going to trust Obama if he says that Jon Tester is a good guy. Same with Arkansas, Missouri, Louisiana, Nebraska, and North Dakota -- and that's where the marginal Democrats in the Senate come from.
To some small extent, and around the margins, a president can affect public opinion. It's a tricky business, however. Some believe that the best strategy is to stake out an extreme position and negotiate towards a new, left-shifted center, but it's also possible that such a strategy just winds up with a lot of people entirely dismissing that politician as an irrelevant extremist.
The first thing, however, to understand is that legislative outcomes are mostly not about strategy, and certainly not about toughness: they're about numbers, and rules of the game. The rules of this game say that nothing becomes law without a majority in the House and, most likely, a supermajority in the Senate -- but certainly a majority in the Senate. As Yglesias says, that means that the real game is about nudging the Testers and Hagans and Conrads a bit out of their comfort zones, and where exactly the numbers fall in all of that. It's not about whether Barack Obama (or Nancy Pelosi, or even Harry Reid) is "really" trying to get a liberal bill.