Pentagon spokesman John Kirby, right, speaks accompanied by U.S. Army Major Gen. William Taylor, Joint Staff Operations, during a media briefing at the Pentagon, Tuesday, Aug. 17, 2021, in Washington. Credit: Alex Brandon / AP

WASHINGTON — The Pentagon is holding fast to a deadline to get U.S. citizens and Afghan allies out of Afghanistan by Aug. 31 even as lawmakers of both parties are pressuring President Joe Biden to extend the effort.

“The mandate by the president is to complete this mission by the 31st of August,” Pentagon press secretary John Kirby said. “That’s the target we’re shooting for. I won’t speculate about any possible different decisions going forward.”

Kirby said any extension of that timetable “would have to be a decision made by the commander in chief.”

More than 40 House lawmakers spanning the political spectrum from progressive Democrats to conservative Republicans are imploring Biden to keep U.S. forces in Afghanistan until they finish evacuating those fleeing the Taliban. The bipartisan nature of their effort underscores the growing unease on Capitol Hill about the United States’ messy withdrawal amid the Taliban’s rapid rise in the country.

“The United States must do everything possible to securely hold the airport in Kabul until the rescue mission is complete and our citizens, allies, and vulnerable Afghans have had an opportunity to leave,” the lawmakers wrote in a Tuesday letter to Biden. “We trust that the previous August 31st deadline you imposed on our military mission will not apply to this effort, and that we will stay as long as is necessary to complete it.”

The letter was led by Democratic Reps. Tom Malinowski of New Jersey and Jason Crow of Colorado and includes many lawmakers who have served in Afghanistan.

Others who signed the letter include Democrats who have long agitated to end the Afghan conflict, including Barbara Lee of California, the only lawmaker to vote against the war authorization in 2001, Jim McGovern of Massachusetts and Pramila Jayapal of Washington. They are joined by Elise Stefanik of New York, the third-ranking House Republican, and Dan Crenshaw of Texas among other GOP House members.

Pentagon officials on Wednesday said the military would hold the airport until the end of the month to evacuate as many people as possible.

There are still 11,000 “self-identified” U.S. citizens in Afghanistan, according to White House press secretary Jen Psaki. There are several times that many applicants for the Special Immigrant Visa program and other refugee programs, according to human rights groups.

Kirby said that there is capacity to airlift between 5,000 and 9,000 people a day.

But lawmakers said that the challenge goes beyond just securing the airport and extends to ensuring that evacuees can move safely past a perimeter set up by the Taliban around the airport. They urged Biden to make clear to the Taliban that they will face “grave consequences” if they attempt to interfere with the evacuation.

“We will need to be clear with the Taliban that they must allow safe passage of Afghans needing evacuation to the airport, and that they will face grave consequences if they threaten our troops or impede our evacuation efforts,” the lawmakers wrote.

Lawmakers also urge the administration to allow Afghan nationals applying for Special Immigrant Visas to stay at the airport “as long as necessary” so they don’t return to Kabul and risk detection by the Taliban.

The tone and timing of the letter, coming after multiple congressional committees announced their intention to probe the administration’s withdrawal plans, illustrates the widening gulf between Capitol Hill and the White House on the Afghanistan pullout.

“It would be unconscionable and devastating to our credibility to leave our allies behind, given the commitments we have made,” the lawmakers write. “We should not consider ourselves bound to any past commitments we have made to the Taliban, who have never fully lived up to their part of the bargains they struck with us.”

“All that should matter now is our moral obligation and strategic interest to help those who helped us, and to stand by the Afghans who bet their lives on the future we promised,” the letter concludes.

Story by Daniel Flatley and Travis Tritten, Bloomberg News