PRESIDENT OBAMA struck a “mission accomplished” tone when he greeted Nouri al-Maliki at the White House last week, heaping praise on the Iraqi prime minister and declaring that he “leads Iraq’s most inclusive government yet.” It didn’t take long for those words to boomerang. No sooner had Mr. Maliki returned to Baghdad than he launched what looks like an attempted coup against the country’s top Sunni leaders. Though the outcome is still in doubt, Iraq’s fragile political order appears in danger of crumbling just days after the departure of U.S. troops.

Mr. Maliki’s strike took the form of criminal charges against Vice President Tariq al-Hashimi, a Sunni known for his attempts to find accord with Shiite leaders. Three security guards arrested last week were paraded on state television Monday, where they confessed to acts of terrorism and alleged that Mr. Hashimi had directed them. Mr. Maliki, meanwhile, asked parliament for a no-confidence vote against Deputy Prime Minister Saleh Mutlaq, another Sunni. Sunni members of parliament and cabinet ministers responded by suspending their work — threatening a governmental collapse.

We haven’t seen enough to judge the charges against Mr. Hashemi, and few Sunni or Shiite leaders are free of any link to the violence that has wracked Iraq since 2003. But both the timing and the televised form of Mr. Maliki’s charges against the vice president were blatantly political. They followed what has been a mounting campaign by the prime minister, a Shiite with close ties to Iran, against perceived Sunni enemies. Hundreds of former members of Saddam Hussein’s Baath party have been arrested in recent weeks. Security forces controlled by Mr. Maliki have surrounded the compounds of Sunni leaders in Baghdad.

The Obama administration appears blindsided by the crisis. It shouldn’t be so surprised. It risked just such a breakdown when it disregarded the recommendation of its military commanders that some U.S. forces remain in Iraq to help guarantee against a return to sectarian conflict. Sunni and Kurdish leaders also urged U.S. officials to broker a deal for a stay-on force with Mr. Maliki; now they say their worst fears may be coming to pass. “The Americans pulled out without completing the job they should have finished,” Iyad Allawi, the leader of the secular political bloc supported by most Sunnis, told the Reuters news agency Tuesday.

The U.S. withdrawal was forced in part by a deal struck by the Bush administration, as well as domestic pressure on Mr. Maliki from Iran’s proxies. But White House aides who argued that no stay-on force was necessary will now see their argument tested. U.S. diplomats in Baghdad are trying to help Iraq’s Kurdish president and foreign minister defuse the incipient conflict; Vice President Biden was on the phone Tuesday to Mr. Maliki and the Sunni speaker of parliament. Washington’s leverage includes the promised sale to Mr. Maliki’s government of F-16 warplanes and training for Iraqi pilots.

Mr. Maliki has said he wishes to maintain a strategic partnership with the United States. If that’s true, Mr. Obama might still rescue the situation by delivering the message he failed to communicate in public last week: Such an alliance cannot be maintained with an Iraqi government that pursues a sectarian agenda or seeks authoritarian power.