As he explained to the country Tuesday afternoon, President Biden has decided to stick with his Aug. 31 deadline for withdrawing all U.S. forces from Kabul, contrary to requests, urgings and advice he has received from allied governments and members of Congress in both parties. The security threat on the ground makes it imperative, he said. Now, there may be only three or four days left for the gigantic airlift currently underway, because time must be left to fly out U.S. and other troops securing the airport themselves. Indeed, some troops have started leaving already. Meanwhile, the Taliban set up a new blockade of the airport road in Kabul to prevent more Afghans from leaving. If Mr. Biden opposes that, he did not say so in his speech.

Mr. Biden, in short, has accepted a series of conditions that seems to make it much more difficult to keep the promises of evacuation he has made or strongly implied. That starts with his top priority, which is, as he put it on Aug. 20, “any American who wants to come home, we will get you home.” Though several thousand U.S. citizens may have been airlifted, the Biden administration itself seems unsure how many are in the country — though the president said Secretary of State Antony Blinken will report that data Wednesday.

To a second group of people, Afghans who worked with the United States and fear being targeted by the Taliban as a result, Mr. Biden has said, “We’re going to do everything — everything that we can to provide safe evacuation.” Even before the Taliban’s new posture, however, the Wall Street Journal had reported that “Afghans who were employed by the embassy or other U.S. agencies in Afghanistan haven’t yet been evacuated in significant numbers.”

And then come the people Mr. Biden has called “Afghans who otherwise are at great risk” — women’s rights activists, local journalists, university faculty, all the people who made life plans banking on the U.S. commitment to the “nation-building” project the president has just disavowed. Of these, Mr. Biden said to George Stephanopoulos of ABC News, “As many as we can get out, we should.” Their prospects seem grim indeed, judging by desperate reports from the ground, and from those in the United States and elsewhere who are trying, mostly without success so far, to help them get access to the airport.

Mr. Biden also said he has asked the Pentagon and State Department to draw up “contingency plans to adjust the timetable should that become necessary.” The ray of hope in all of this is that the United States has ramped up the exodus substantially in recent days, to number 11,600 people Tuesday, and 70,700 since Aug. 15, when the Taliban seized Kabul. That fast pace, coupled with far greater access for vulnerable Afghans, would be necessary for Mr. Biden to fulfill even partially the expectations of evacuation that he has raised.