The remarks also reflected the disarray that has surrounded the president’s decision, which took his staff and foreign allies by surprise and drew objections from the Pentagon that it was logistically impossible and strategically unwise. Defense Secretary Jim Mattis resigned within hours of the announcement, and the Pentagon chief of staff, Kevin M. Sweeney, said on Saturday evening that he was also leaving.

While Mr. Bolton said on Sunday that he expected American forces to eventually leave northeastern Syria, where most of the 2,000 troops in the country are based for the mission against the Islamic State, he began to lay out an argument for keeping some troops at a garrison in the southeast that is used to monitor the flow of Iranian arms and soldiers. In September, three months before Mr. Trump’s announcement, Mr. Bolton had declared that the United States would remain in Syria as long as Iranians were on the ground there.

Asked on CBS News’s “Face the Nation” if Mr. Bolton’s comments amounted to an admission that Mr. Trump had made a mistake, Senator Lindsey Graham, a South Carolina Republican who at times has been one of the president’s staunchest supporters, said, “This is the reality setting in that you’ve got to plan this out.”

Mr. Graham, who described the dangers of making the announcement first and then considering the longer-term implications, added, “The president is slowing down and is re-evaluating his policies in light of those three objectives: Don’t let Iran get the oil fields, don’t let the Turks slaughter the Kurds, and don’t let ISIS come back.”

The move to reverse course on Mr. Trump’s promised swift withdrawal picked up in recent days, even as Mr. Bolton worked to avoid openly confronting the president the way Mr. Mattis did. On Friday, in a briefing for reporters about a forthcoming trip to the Middle East by Secretary of State Mike Pompeo, a senior State Department official said there was no fixed timetable for the American withdrawal.