Iraqi PM Nouri al-Maliki is giving powerful Shiite cleric Moqtada Sadr's forces three days to surrender in Basra, as clashes between Maliki's security forces and Sadr's Mahdi Army -- in which the U.S. intervenes on Maliki's side -- escalate. But with the U.S. happy about the now-abrogated Sadrist ceasefire, why is the U.S. military getting involved? The Washington Post isn't sure:

It was unclear why U.S. forces would take part in a broad armed challenge to Sadr and his thousands-strong militia on the eve of Petraeus's assessment, which the Bush administration has said would greatly influence its decision on whether to draw down troop levels.

Here's an answer. As long as Maliki is in the prime minister's chair, and as long as we proclaim the Iraqi government he leads to be legitimate, Maliki effectively holds us hostage. He says, "I need to go after Sadr. The situation is unacceptable! In Basra, he threatens to take control of the ports, and in Baghdad, he's throwing my men out of their checkpoints. Would you allow the Bloods or the Crips to take over half of Los Angeles?" And as soon as he says that, we're trapped. It simply is not tenable for Petraeus to refuse a request for security assistance from the Prime Minister to deal with a radical militia.

Now, some of my Iraq-watcher friends of mine point out that this is absurd. "Sadr is, of course, a thug," they say, "but he's a nationalist. And he's far less beholden to Iran than the Islamic Supreme Council of Iraq or Maliki's Da'wa Party -- both of whom we're supporting! And most importantly, Sadr remains perhaps the most popular figure in Shiite Iraq. Petraeus can do business with him. This doesn't make any sense!" And they're right. It doesn't. But as long as we sponsor the Iraqi political process -- and a Sadrist doesn't actually become premier himself -- this will keep happening.

Some might say it's time to dump Maliki. I suspect that's what's behind this brief passage in the New York Times:

The Basra operation, which senior Iraqi officials had been signaling for weeks, is considered so important by the Iraqi government that Mr. Maliki traveled to the city to direct the fighting, several officials said.

That reads to me like some officials are preparing to throw Maliki under the bus. After all, if he's personally responsible for the fighting, and it goes badly, then his Shiite rivals can maneuver a way to put forward a new premier. That is, of course, how Maliki himself came to power in the spring of 2006. And if the Iraqis themselves do it, we have little choice but to acquiesce.

But. The dangers of picking and choosing who the Iraqi premier should be outweigh any imperial temptations we may feel. We'll be just as responsible for Prime Minister Next-Up's mistakes as we are for Maliki's. And the Iraqis will never trust any leader that foreigners pick for them. In what's shaping up to be the Second Sadrist Intifada, you go to war with the prime minister you have, not the prime minister you might want.