The liberals are angry, and not without reason. You can imagine a world in which "centrist" Senators used their awesome deal-making powers to forge compromises that incorporate ideas from the left and right alike. A world in which moderate "gangs," in David Brooks' formulation, actually put meat on the bones of Barack Obama's promise to end politics as usual. A world in which Susan Collins, Ben Nelson, Arlen Specter and Joe Lieberman emerged as ardent champions of, say, a stimulus approach divided evenly between billions in Keynesian spending and billions for the sort of payroll tax proposal that people like Larry Lindsey and Greg Mankiw have been championing - or some similarly wonky, high-concept policy compromise. A world of bipartisanship and postpartisanship and everything in between.

But that's not the world we live in. In this world, centrist Senators exist to take politics as usual - whether it's tax cuts in Republican eras, or spending splurges in Democratic ones - and make it ever so slightly more fiscally responsible. So if the GOP wants, say, $500 billion in tax cuts, the country clearly needs $400 billion in tax cuts - but not a penny more! And if the Democrats want $900 billion in stimulus, then the best possible policy outcome must be ... $800 billion in stimulus! To read this Arlen Specter op-ed, justifying both the stimulus package and the cuts the "gang of moderates" have attempted to impose, is to encounter a mind incapable of thinking about policy in any terms save these: Take what the party in power wants, subtract as much money as you can without infuriating them, vote yes, and declare victory.

Now fiscal responsibility is generally a good thing, and so a centrism mindlessly focused on tweaking legislation away from deficit spending has its uses. But what Nelson, Collins, Specter and Co. have done isn't a new kind of politics. It's the definition of politics as usual. And in this particular case, there's a reasonable argument that it's actively pernicious - that if you can't shrink the stimulus package much more substantially than the centrists have done, you shouldn't shrink it at all. There's a case to be made for a stimulus that's radically different than the one we have now; there's a case to be made for a stimulus that's like the one we have now, but a great deal smaller and more targeted; and there's a case to be made for a stimulus that's absolutely gargantuan. But thanks to the centrists, we're getting the cheapskate version of the gargantuan version: They've done absolutely nothing to widen the terms of debate about what should go into the bill, and they've shaved off just enough money to reduce its effectiveness if Paul Krugman is right - but not nearly enough to make it fiscally prudent if the stimulus skeptics are right. 

This means that if the damn thing doesn't work, we won't even know whom to blame. But it wouldn't be crazy to start by blaming the centrists.