WASHINGTON — Over the past four years, American military planning in Iraq has counted on working with Prime Minister Haider al-Abadi, a moderate Shiite Muslim who has managed to rebuild the country’s army, restore sovereignty and partner with both the United States and Iran to defeat the Islamic State.
But the results of the weekend’s national elections in Iraq have torn the American assumptions asunder.
Huge gains in Parliament were made by a party led by the anti-American cleric Moktada al-Sadr, whose implacable opposition to the presence of United States troops in Iraq was a top reason Washington withdrew its combat forces in 2011.
Now, President Trump and the Pentagon must decide whether the United States can move ahead with plans to leave a residual force of about 4,500 American troops in Iraq after the war against the Islamic State.
The group, also known as ISIS, is largely gone from the areas of Iraq that it occupied as recently as last year. But military planners are all too aware of what happened after the American troops left in 2011, opening space for the Islamic State’s rise as it was fueled by minority Sunnis who were alienated by the ruling Shiite government of Nuri Kamal al-Maliki, then the prime minister.
In 2014, the Islamic State rolled across Iraq, easily defeating the country’s army and controlling much of its northern and western regions. Ensuring that history is not repeated is a top American priority, senior State Department and Pentagon officials said.
For the Trump administration, that means trying to find a way to a working relationship with Mr. Sadr. Administration officials sought this week to focus on positive aspects of the election.
“Not that long ago, ISIS had controlled large swaths of that country,” said Heather Nauert, the State Department’s spokeswoman. “And the fact that they were able to pull off elections that were relatively free of violence is certainly a pretty amazing feat and a testament to the Iraqi people.”
Defense Secretary Jim Mattis told reporters that Trump administration officials “stand with the Iraqi people’s decisions.”
“It’s a democratic process at a time when people, many people, doubted that Iraqis could take charge of themselves,” Mr. Mattis said on Tuesday.
As a young man, Mr. Sadr led a Shiite militia that targeted American troops in Iraq. He fled to Iran to study in Qom, a revered Shiite religious center, before returning to Iraq in 2011 as a cleric and strident Iraqi