“I want to get out — I want to bring our troops back home,” Mr. Trump said on Tuesday during a news conference with leaders of Baltic nations. “It’s time. We were very successful against ISIS.”
The United States has been aiding a military campaign in Syria that has reclaimed much of the territory once under the control of the militant group. But while Mr. Trump has expressed enthusiasm for battling ISIS, he is reverting to the “America First” posture he pressed as a candidate, hoping to separate the United States from foreign involvement and military adventures abroad.
The decision comes as Mr. Trump’s national security team is in flux, and has been divided over what to do in Syria. The president ousted his secretary of state, Rex W. Tillerson, last month, and his national security adviser, Lt. Gen. H.R. McMaster, is soon to depart after Mr. Trump decided to replace him with John R. Bolton.
While Mr. Trump has pressed intensively to withdraw troops and unwind American involvement, Pentagon officials argued strenuously in recent days against a pullout of all United States troops from Syria. They pointed to the rise of the Islamic State in Iraq after former President Barack Obama withdrew troops from there as a precedent they said laid the groundwork for the militant organization to flourish there.
Defense Department officials say that sacrifices made by the American military in Syria could be washed away if troops leave precipitously.
“A lot of very good military progress was made over the last couple years,” said Gen. Joseph L. Votel, the top officer at the military’s Central Command, during a conference in Washington on Tuesday.
“But again, the hard part I think is in front of us, and that is stabilizing these areas, consolidating our gains, getting people back into their homes, addressing the long-term issues of reconstruction and other things that will have to be done,” General Votel said.
Col. Ryan Dillon, the spokesman for the American-led coalition in Iraq and Syria, said that the Islamic State still holds territory in the mid-Euphrates River Valley, and noted that trying to rout the remaining militants has proved difficult as offensive operations have all but ceased in the area.
The slow pace of the campaign stems from losing Syrian Kurds — the American military’s key ally in the fight against the Islamic State — to a new fight against Turkish troops in the northwestern corner of the country.
Operations are “not happening at the pace it was about a month and half ago,” Colonel Dillon said.
The president surprised even his own advisers last week when he said publicly that the United States would soon remove troops from Syria.
Mr. Trump was in Ohio delivering remarks on trade policy when he veered off topic and said, “We’re knocking the hell out of ISIS,” and added: “We’ll be coming out of Syria, like, very soon. Let the other people take care of it now.”
The following day, Mr. Trump directed the State Department to halt financial recovery assistance for Syria while his administration reconsidered its policy.
By Tuesday, he said he was consulting with allies and would soon be ready to announce a new policy. The White House said the president spoke on Monday with King Salman of Saudi Arabia, and “discussed joint efforts to ensure the enduring defeat of ISIS and counter Iranian efforts to exploit the Syrian conflict to pursue its destabilizing regional ambitions.”
In his news conference on Tuesday, Mr. Trump gave a sharper account of the conversation, suggesting that the king had pressed him to maintain the American troop presence in Syria as he objected.
“I said, ‘Well, you know, you want us to stay, maybe you’re going to have to pay,’ ” Mr. Trump said.