The scale of the attack — initial reports indicate four U.S. service members were killed and three were wounded — and Islamic State’s claim of responsibility potentially complicate Trump’s plan to leave Syria. Trump initially declared the group defeated in December, though he later qualified the claim to say Islamic State had lost territorial control of the self-proclaimed caliphate it once held.

Republican Senator Lindsey Graham of South Carolina, a prominent Trump ally who has criticized the Syria withdrawal plan, suggested the president’s stance emboldened Islamic State fighters and encouraged such attacks. He urged Trump to reconsider.

Trump’s statements “set in motion enthusiasm by the enemy we’re fighting” and “make people we’re trying to help wonder about us, and as they get bolder, the people we’re trying to help are going to get more uncertain,” Graham said at a Judiciary Committee hearing. “I saw this in Iraq. And I’m now seeing it in Syria.”

Read a QuickTake on who’s still fighting in Syria’s eight-year war

Vice President Mike Pence, speaking at the State Department, didn’t mention the attack but repeated Trump’s claim of victory. “The caliphate has crumbled and ISIS has been defeated,” he said.

“As we begin to bring our troops home, the American people can be assured, for the sake of our soldiers, their families, and our nation, we will never allow the remnants of ISIS to reestablish their evil and murderous caliphate – not now, not ever,” Pence said later in a statement.

A suicide bomber wearing an explosive vest attacked international forces patrolling in the northern town of Manbij, according to Islamic State’s self-styled Amaq news agency, which is used by the group to claim attacks around the world.

The Syrian Observatory for Human Rights, which monitors the Syrian civil war through activists on the ground, says the blast killed at least 16 people, including two American soldiers.

The White House referred questions about the attack to the Defense Department, which said service members were killed by an explosion while on “routine patrol,” but didn’t say how many.

U.S. Withdrawal

The attack, if proven to be carried out by Islamic State, would be the latest in a series of stumbling blocks in Trump’s efforts to exit Syria. The president’s decision — apparently made during a phone call with his Turkish counterpart last month — has already faced serious pushback from within the U.S. administration, leading to the resignation of Defense Secretary James Mattis. A suicide bombing by the jihadist group could bolster the argument that America’s job in Syria remains unfinished.

Trump’s Syrian Detente With Erdogan Masks a Rot That Runs Deep

Republican Senator Rand Paul, who has long advocated for an American withdrawal, said he’d visit the White House on Wednesday to urge Trump to stick with his plans to pull troops out.

“I will tell him ‘stay the course,”’ Paul said in an interview. “The American people are tired of war, bring our troops home.” He dismissed Senator Graham’s comments about Trump’s policy emboldening Islamic State.

“They’re probably going to be fighting each other for another 1,000 years,” Paul said. “If you’re going to wait for a time when perfect peace breaks out in the Middle East, you’ll never leave.”

The confusion over U.S. plans to exit Syria has stoked tensions with NATO ally Turkey; the town of Manbij is at the heart of the dispute over U.S. support for Kurdish YPG fighters. The U.S. and Turkey agreed on a road map last year to have the fighters withdraw from the area. While the U.S. says no timeline was attached to the plan, Ankara wants the Kurds out fast, saying they are linked to a militant Kurdish separatist group that Turkey has been battling for decades.

While Trump initially claimed the withdrawal was justified by the defeat of Islamic State, he later made clear that remnants of the group remained and should be eradicated by other countries’ forces as the U.S. left. Turkish President Recep Tayyip Erdogan has said that Turkey could take on that role, but has also said that an operation could target the U.S.-backed Kurdish forces, prompting warnings from American officials and from Trump.

Islamic State has lost almost all of the land it once held under its caliphate. The group swept through Iraq and Syria in 2014, conquering large chunks of territory before its major strongholds fell at the end of 2017. The U.S.-backed coalition, Iraqi and Syrian government forces, Syrian rebels, Russian airstrikes and Iranian-allied militias have all targeted the group. DM