Chairman of the Joint Chiefs of Staff Gen. Mark Milley said he will not resign after President Biden ignored his recommendation to keep a presence of at least 2,500 U.S. troops in Afghanistan, saying to do so would be an "incredible act of political defiance."

Milley testified Tuesday before the Senate Armed Services Committee, alongside Defense Secretary Lloyd Austin and head of U.S. Central Command Gen. Kenneth McKenzie, saying his personal opinion was to maintain troops in Afghanistan. 

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Milley said that while he would not share his "personal" recommendations he made to the president, his assessment was, "back in the fall of 2020, and remained consistent throughout, that we should keep a steady state of 2,500 and it could bounce up to 3,500, maybe, something like that, in order to move toward a negotiated solution." 

Biden and White House officials have said repeatedly that no military leaders advised him to leave a small military presence behind, with the president, himself, telling ABC News in August that "no one" recommended a 2,500 troop presence that he could "recall." 

Milley also testified that he was not contacted for his military assessment on whether to maintain a troop presence in Kabul beyond Aug. 31 until Aug. 25 – a time in which he and other military officials came to the "unanimous" conclusion to complete the full withdrawal. 

Kabul fell to the Taliban on Aug. 15.

Sen. Tom Cotton, R-Ark., slammed the Biden administration for waiting "10 days to ask officers" for their assessment. 

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"I suspect the answer would have been a little different had you asked them 16 days out, not five days out," Cotton said, moving on to press Milley on why he has not resigned after his recommendations were "rejected." 

"Senator, as a senior military officer, resigning is a really serious thing – it's a political act – if I'm resigning in protest," Milley said. "My job is to provide advice – my statutory responsibility is to provide legal advice or best military advice to the president, and that's my legal requirement. That's what the law is." 

Milley added that the president "doesn't have to agree with the advice," and said he "doesn't have to make those decisions just because we're generals." 

Chairman of the Joint Chiefs of Staff Gen. Mark Milley attends a Senate Armed Services Committee hearing on the conclusion of military operations in Afghanistan and plans for future counterterrorism operations, Tuesday, Sept. 28, 2021, on Capitol Hill in Washington. (AP Photo/Patrick Semansky, Pool) (AP Photo/Patrick Semansky, Pool)

"It would be an incredible act of political defiance for a commissioned officer to just resign because my advice is not taken," Milley said. "This country doesn't want generals figuring out what orders we are going to accept and do or not. That's not our job." 

He added, on a personal note, that "my dad didn't get a choice to resign at Iwo Jima, and those kids at Abbey Gate don't get a choice to resign." 

"I'm not going to turn my back – they can't resign," Milley said. "So I'm not going to resign. There's no way." 

"If the orders are illegal, we're in a different place," Milley said. "But if the orders are legal from civilian authority, I intend to carry them out." 

McKenzie also testified Tuesday that he recommended the U.S. "maintain 2,500 troops in Afghanistan." 

McKenzie said he made a similar recommendation in the fall of 2020 under the Trump administration, which also had intentions to withdraw all U.S. troops from Afghanistan, saying, at the time, he recommended the U.S. maintain at least 4,000 troops.

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"I also have 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 testified. 

Austin was asked whether the president received the personal recommendations from his top military advisers like Milley and McKenzie. 

"Their input was received by the president and considered by the president for sure," Austin testified. 

The hearing comes nearly a month after the Biden administration, on Aug. 31, withdrew all U.S. military assets from the region after having a presence there for 20 years following the attacks on Sept. 11, 2001. An Aug. 26 suicide bombing took the lives of 13 U.S. service members – including 11 Marines, one Navy sailor and one Army soldier. Eighteen other U.S. service members were wounded. The bombing also left more than 150 civilians dead.

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As the Biden administration began the withdrawal of military assets, provincial capitals across Afghanistan began to fall to the Taliban. By mid-August, the Taliban attained control of two-thirds of Afghanistan. And by the time the U.S. withdrew all U.S. troops from the country on Aug. 31, Kabul had also fallen to the Taliban. In mid-August, U.S. intelligence assessments projected the capital city could fall to the Taliban within 90 days.