As I said in my speech reaction post, I don't think the tepid endorsement of the bill formerly known as energy/climate really matters very much: what matters is what comes next. And I can't see any real downside for the president if he chooses to invite everyone back to Blair House for another summit.
First of all, the Republicans might refuse. That would be a victory for the president.
Second, it's possible that some Republicans might actually show up looking to make a deal. Obviously, that's a victory for the president.
Third, and most likely, the Republicans would repeat their health care performance: they would show up with focus-group-tested talking points that wouldn't stand up very well to the president's knowledge of the subject, especially since he's the one who gets to control the microphone (and, yes, Obama should insist on the same format as the health care summit, take it or leave it -- again, what are they going to do?).
Now, mostly the effects of a summit would be minor. It would probably make Democrats feel good, and I suspect would make for some rather uncomfortable moments for Lindsey Graham, Susan Collins, and other Republicans who have at times claimed that they wanted a bill -- which, again, would make Democrats feel good. I don't think that spin is all that important, but I do think that (for whatever incremental amount it's worth) that Obama is much better off if everyone is talking about a bill than if they're talking about the oil spill.
Mostly, however, it would be worthwhile as a signal that Obama and the Democrats are really serious about getting a bill this year. It is true that we're not at an analogous stage in the process in terms of the parliamentary situation, but I think we are at a similar stage in terms of the question of whether the thing is really going forward or not. Sending a strong, unambiguous signal that something is going to pass could, I think, matter a bit. Right now, I think most Democrats in the Senate probably believe there's a fair chance they can duck the issue entirely. Forcing the issue will force them off the fence, and push them to make whatever deals they need to make to vote for the bill. To the extent that downgrading or removing climate from the bill means that Republicans might vote for it, the same is true for them.
That's all if there's a real chance for a bill, and assuming that Obama wants one. If not -- if he'd rather have the issue -- it sure seems to me that a summit works, too. Again, I'm really not seeing a down side (anyone? explain it to me in comments). I don't know if that's where the administration is headed, but the president is using the same rhetoric about accepting good Republican ideas that he used for health care, and so maybe that's where they're headed. If so: good choice.