It seems to me the actual big question here was whether Harry Reid would put Kent Conrad on the Joint Select Committee or not. I have to say I was wrong; I figured that Conrad, a longtime and generally honest deficit idealist, would be on it. Instead, it's John Kerry and Patty Murray with Max Baucus. I'd expect all three of Nancy Pelosi's selections to be solid liberals, so if there's going to be a 7-5 majority made up of all the Republicans and one defecting Democrat, Baucus is the one to watch. It's possible, but quite unlikely, I'd say -- although that coalition probably could get a simple majority in the Senate. After all, as liberals have noted already Baucus voted against the Bowles/Simpson plan as a member of the group, so he doesn't always prefer some deal to no deal. Overall, he'll be by far the most moderate out of the twelve, but he's not a Joe Manchin.
What is likely is that Baucus will want to put together a center faction that can actually achieve something. Whether there's any room to do so depends, of course, on who the GOP puts on the committee. Odds are that there won't be anyone willing to make that sort of deal, and even if there was it's very unlikely it could command 7 votes.
That leaves a real compromise deal that can win the support of most or all of the committee, but that seems awful difficult to see (as Stan Collender argued right away last week). There's just no way that the Republicans put on this committee are going to be willing to commit to a dime of new taxes, and if that's the case then Democrats would almost certainly be happier with the trigger than an any other all-spending deal.
Does that mean the trigger will actually be pulled? Not necessarily; there could be a deal outside of the committee. Such a deal could repeal the trigger and replace it with...well, we don't know. Any such legislation would be a simple bill, subject to filibusters and any other procedural difficulties. But I think Jonathan Chait had this right; the trigger is more likely than a Joint Select Committee deal, but just because the trigger goes into effect at the deadline doesn't mean that it stays in effect in the long run. I'll add: if the House sticks to its previous pattern, expect them to pass their own alternative sometime before the deadline, but one that winds up far worse for the Democrats than the automatic cuts in the trigger.
One more thing -- don't forget that we will have a showdown over FY 2012 appropriations before all of this happens. At least, the first round of that showdown.