Biden, Setting Afghanistan Withdrawal, Says ‘It Is Time to End the Forever War’

Mr. Bush opted not to publicly second-guess Mr. Biden’s decision.

“As he has maintained since leaving office, President Bush will decline to comment on private phone calls or his successors,” said Freddy Ford, his chief of staff.

A series of Afghan governments have failed to sustain control over vast sections of the country, the essence of the American military’s “clear, hold, build” strategy for years after the initial invasion. While a succession of Afghan leaders, supported by the United States and its allies, promised to fight corruption, end the drug scourge and establish stable governance, all of those gains have proved fragile at best.

Women have taken a more prominent role in the government, and girls have been educated on a scale not seen before the war began. But the future of those gains is in doubt if the Taliban gain more ground.

In a statement on Twitter, President Ashraf Ghani of Afghanistan said his country “respects the U.S. decision and we will work with our U.S. partners to ensure a smooth transition.” He added that his country’s security forces were “fully capable of defending its people.”

But in private, Mr. Ghani has fumed about the American decision, according to people who have spoken to him. He fears that it will embolden the Taliban, and give them little to no incentive to stick to the terms of the agreement they reached a year ago with Mr. Trump. And many around Mr. Ghani fear that his own government, already diminished in influence, could fall if the Taliban decide to try to take Kabul, the capital.

“Just because we withdraw from Afghanistan doesn’t mean the war ends,” said Lisa Curtis, a top Trump national security official who dealt with Afghanistan. “It probably gets worse.”

Mr. Biden is the first president to have rejected the Pentagon’s recommendations that any withdrawal be “conditions based,” meaning that security would have to be assured on the ground before Americans pulled back. To do otherwise, military officials have long argued, would be to signal to the Taliban to just wait out the Americans — after which they would face little opposition to taking further control, and perhaps threatening Kabul.