Sen. Tom Cotton, R-Ark., asked Chairman of the Joint Chiefs of Staff Gen Mark Milley why, given that advice to leave 2,500 troops behind, wasn't taken by the president, he hasn't resigned. Milley said it would be "an incredible act of political defiance for a commissioned officer to just resign because my advice is not taken."

"As a senior military officer, resigning is a really serious thing. It's a political act if I'm resigning in protest," Milley said. "The president doesn't have to agree with that advice, he doesn't have to make those decisions just because we're generals. And it would be an incredible act of political defiance for a commissioned officer to just resign because my advice is not taken."

Appearing to break publicly with President Joe Biden and former President Donald Trump, Milley was later asked about the pace of withdrawal and said that he was opposed to putting a date to military withdrawals, as "two presidents in a row" have done, saying conditions should always be in place. He added, though, that risks to Americans would have increased if the U.S. remained past Sept. 1.

"Senator, as a matter of professional advice, I would advise any leader, don't put date-certains on end dates. Make things, conditions-based. Two presidents in a row put dates on it. I don't think -- that's, my advice, don't put specific dates," Milley said.

The nation’s military leaders -- Secretary of Defense Lloyd Austin, chairman of the Joint Chiefs of Staff Gen. Mark Milley and Gen. Kenneth McKenzie, commander of U.S. Central Command, have all said their recommendations on the U.S. withdrawal from Afghanistan were given to President Biden and heard.

GOP Sen. Tom Cotton, R-Ark., pressed Milley on whether he specifically recommended to Biden that 2,500 troops stay in Afghanistan, as McKenzie had suggested. Milley wouldn’t comment on his personal conversations but gave his assessment from last fall and added he’s "always candid" with the president.

"My assessment was back in the fall of '20 and remained consistent throughout that we should keep a steady state of 2,500, could bounce up to 3,500, something like that, to move towards the negotiated gated solution," he said.

Cotton then turned to Austin and raised the question to him, citing Biden’s interview with ABC News’ George Stephanopoulos last month in which he said that no military leader advised him to leave a small troop presence in Afghanistan.

"Senator Cotton, I believe that -- first of all, I know the president to be an honest and forthright man. And secondly," Austin said, before Cotton interrupted him to ask again if their recommendations got to Biden.

"Their input was received by the president and considered by the president for sure," Austin said. "In terms of what they specifically recommended, senator, they just, as they just said, they're not going to provide what they recommended in confidence."

Gen. Kenneth McKenzie, commander of U.S. Central Command, said his recommendation was to keep 2,500 troops in Afghanistan beyond Biden's Aug. 31 deadline, believing a full withdrawal would lead to inevitable collapse.

"I recommended that we maintain 2,500 troops in Afghanistan. And I also recommended earlier in the fall of 2020 that we would maintain 4,500 at that time -- those are my personal views. I also had a view that the withdrawal of those forces would lead inevitably to the collapse of the Afghan military forces, and eventually the Afghan government," McKenzie said.

Biden told ABC News' George Stephanopoulos in an exclusive interview in August that "no one" that "he can recall" advised him to keep a force of 2,500 troops behind.

Earlier in the hearing, both McKenzie and Gen. Mark Milley, chairman of the Joint Chiefs of Staff, affirmed to the committee that the Doha agreement with the Taliban hurt the morale of Afghan security forces.

"The Doha agreement did negatively affect the performance of the Afghan forces," McKenzie said.

Gen. Mark Milley, chairman of the Joint Chiefs of Staff, defended the U.S. military’s withdrawal from Afghanistan while acknowledging the U.S. did not foresee an 11-day takeover by the Taliban, placing some blame on the Afghan government and army.

“\"This has been a 10-year multi-administration drawdown, not a 19-month or a 19-day withdrawal," Milley said in his opening testimony.

He also said that a week after the election he received an order to pull all U.S. troops out of Afghanistan by mid-January, but days later, that order was rescinded.

For the larger part of his opening testimony, Milley took the chance to defend contacts with his Chinese counterparts in the final days of former President Donald Trump’s presidency and offered a "walk-through of all these events" amid reporting he broke the regular chain of command.

"At no time was I attempting to change or influence the process, usurp authority, or insert myself into the chain of command, but I am expected to give my advice and ensure that the president is fully informed," he said.