Criticism over troop withdrawal emerges from beyond the GOP

“If it was a timeline with a strong statement that said, ‘Hey, this is our plan, but no plan survives contact with reality and, of course, we are going to adjust based on conditions on the ground,’ then no problem,” said Michèle A. Flournoy, who served as the undersecretary of defense for policy during Mr. Obama’s first term. “Are the Afghans on the path we have planned for, or are they not? Is the insurgency as we expected, or is it worse? All those things have to be factored in.

“But what I am hearing out of the White House is that ‘hell or high water, this is what we are going to do.’ ”

James N. Mattis, the retired Marine general who oversaw the war in Afghanistan as head of the United States Central Command from 2010 to 2013, said it was particularly unwise to set a public deadline for removing American troops.

“When you set a deadline, you give the enemy a reason for optimism, and in foreign policy, we should be reticent at telling our adversaries in advance what we will not do,” General Mattis said in an interview.