For a president who has looked to the military for affirmation throughout his campaign and presidency and boasted about stocking his cabinet with what he called “my generals,” his decision on Dec. 19 to withdraw quickly from Syria was a significant split from his military and civilian advisers. The criticism from General McChrystal, who commanded American-led troops in Afghanistan from 2009 to 2010, echoed longstanding denunciations by former senior intelligence officials, who have warned that Mr. Trump’s approach to national security is reckless.

But during a surprise trip to Iraq last week, Mr. Trump privately told the commander of American forces in Iraq and Syria, Lt. Gen. Paul J. LaCamera, that the military could have several months to complete a safe and orderly withdrawal, according to two United States officials. And on Sunday, Senator Lindsey Graham, Republican of South Carolina, told reporters that a “pause situation” on the troop withdrawal was in effect.