President Joe Biden's decision to withdraw foreign troops from Afghanistan ushers in a new set of risks for the United States and its military.
What are those risks, and how does the administration hope to mitigate them?
– Does 'withdrawal' equal 'security vacuum'?
Officially, the Pentagon supports the US president's decision to end America's longest war. But many senior US commanders have been voicing their misgivings for months.
General Kenneth McKenzie, head of the US Central Command, recently told AFP that he had "reasons to believe" a withdrawal would allow the resurgence of extremist groups, with the risk of a collapse of the Afghan government.
CIA Director William Burns acknowledged Wednesday that when the United States withdraws, the "US government's ability to collect and act on threats will diminish."
But he promised that the CIA would maintain "capabilities" in Afghanistan.
Retired General David Petraeus, who has operated in Iraq and Afghanistan, said Washington must be "really careful" with its rhetoric on the withdrawal.
"Ending US involvement in an endless war doesn't end the endless war. It just ends our involvement. And I fear that this war is going to get worse," he said.
– Was it dangerous to announce a deadline?
The military had feared putting a date on the US departure, seeing it as a temptation to the Taliban, emboldened by what they see as victory over the world's largest and most technologically-advanced army, to attack troops on the ground without consequences.
Biden has warned the Taliban against any such attempt, and NATO has said in a statement that "any Taliban attacks on Allied troops during this withdrawal will be met with a forceful response."
In addition, the allies were careful to say that the withdrawal would begin on May 1 — the date by which it should have been completed under the Donald Trump administration's agreement with the Taliban.
But they also said it would be completed by September 11, the 20th anniversary of the attacks that prompted the invasion in the first place — and a date already heralded by jihadists groups as a day of victory over the US.
"The chosen withdrawal date plays into the jihadi narrative of a 'crusader occupation' and seems like an error on the part of the Biden administration that could have been avoided," the Soufan Center said in an analysis.
US officials stressed that the deadline was largely symbolic.
"There's not actually a date on the calendar for when we can guarantee you the last trip will be out … it will be no later than the 20th anniversary of 9/11, meaning it could be, as I said before, well before then," one senior administration official stressed.
– What are the logistics of withdrawal?
The US military feared most of all that it would have to leave Kabul in a hurry, and find itself in the same situation as when Saigon fell during the Vietnam War in 1975, immortalized by images of refugees boarding a helicopter on the roof of an apartment building near the US embassy.
Some 2,500 US troops, plus 16,000 civilian contractors and their equipment, must be evacuated from the country — along with some 7,000 NATO soldiers, who depend on the US military for the transport of troops and equipment.
It is therefore a huge and delicate logistical operation that must be carried out, and the military needs at least three months to complete it in an orderly and secure manner, according to a senior US military official.
The Pentagon could send reinforcements temporarily, to ensure the protection of the forces on departure, as during the military withdrawal from Syria started in January 2019 on the orders of Donald Trump.
Defense Secretary Lloyd Austin halfheartedly acknowledged the reluctance of US generals to leave, and by a particular deadline.
"I won't speak for them. What I can tell you is this was an inclusive process, and their voices were heard and their concerns taken into consideration as the president made his decision," he said in Brussels.
– What of US credibility?
With the war at best a stalemate, and the Taliban in the ascendancy after 20 years of fighting, it is easy for them and other enemies of the US to frame this withdrawal as a triumph over a world superpower — a fact not lost on Biden's political opposition, the Republican Party.
Many Republicans have spoken forcefully about the withdrawal's impact on US influence and credibility around the world.
"Withdrawing our forces from Afghanistan by September 11 will only embolden the very jihadists who attacked our homeland on that day 20 years ago," protested Republican Congresswoman Liz Cheney.
"It is a retreat in the face of an enemy that has not yet been vanquished and abdication of American leadership," Republican Senate leader Mitch McConnell said on the Senate floor.