TWO PERSISTENT failings of U.S. foreign policy have been an overdependence on individual leaders, who frequently fail to deliver on American expectations, and a reluctance to accept that an established status quo can’t hold. The Obama administration has committed both those errors in Iraq — and it has done so more than once.

In its zeal to withdraw all U.S. troops in time for President Obama’s reelection campaign in 2012, the administration threw its weight behind then-Prime Minister Nouri al-Maliki, with disastrous consequences. Mr. Maliki’s Shiite sectarianism fractured the fragile political system and opened the way for the Islamic State. In 2014, having pushed for Mr. Maliki’s removal, the administration bet on Haider al-Abadi; now, in its impatience to reduce the Islamic State before Mr. Obama leaves office, it clings to a prime minister who has proved unable to govern the country or reconcile its warring factions.

Mr. Abadi’s impotence was revealed most dramatically over the weekend, when Shiite supporters of anti-American firebrand Moqtada al-Sadr stormed into Baghdad’s walled-off Green Zone and invaded the parliament. Nominally, the protesters were supporting one of Mr. Abadi’s aims, to create a new, technocratic cabinet to replace a corrupt system of dividing ministries according to party and sectarian lines. But Mr. Abadi denounced the invasion, which showed him as unable to control either the political insurgents or the established parties that have repeatedly rejected his reform proposals.

The blowup came at a particularly awkward time for the Obama administration, which had just doubled down on its support for Mr. Abadi during a visit to Baghdad by Vice President Biden. As The Post’s Greg Jaffe reported, an administration briefer told reporters that Mr. Biden’s visit was “a symbol of how much faith we have in Prime Minister Abadi” and expressed optimism that his government was getting stronger.