The second group of Marines arrived in Kabul Saturday to assist with the deteriorating situation in Afghanistan as the Taliban continued to make violent advances across the country. 

Less than 24 hours later, the U.S. embassy in Kabul was evacuated and the country's president had been forced to flee the country as Taliban fighters raised their flag above the city to soon declare it the Islamic Emirate of Afghanistan.

Up to 5,000 troops – including 1,000 paratroopers from the 82nd Airborne Division along with one Army and two Marine Corps infantry battalions – were initially tasked with removing thousands of American diplomatic personnel and Afghan interpreters from Kabul. That mission evolved from evacuation to managing a no-good-outcome scenario that critics fear could resemble the airlift departure of U.S. troops out of Vietnam some 50 years ago. 

Despite the life-threatening situation unfolding in Afghanistan, with American forces believed to still be on the ground amid the chaos, the Pentagon said it is not classifying the undertaking as a "combat mission."

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Retired Marine Corps Major General Arnold Punaro told Fox News on Saturday that he was "not familiar with what technical definition" the Pentagon was relying on, but said the leaders and soldiers on the ground "will totally consider this to be a combat mission."

"First of all, these troops are fully armed and in their full battle gear. They are going into a situation prepared for the worst case. And frankly, that’s what they got to do because they are going to be charged with a mission of protecting American lives, evacuating Americans, evacuating others that they may be told to evacuate, and they have to be prepared for all eventualities."

Punaro, who served in Vietnam and has been involved in evacuation operations, explained that the Pentagon could be looking at the situation in Kabul as a "permissive environment" but warned, "it could very rapidly turn into a non-permissive environment."

Though Pentagon Press Secretary John Kirby told reporters Friday that he did not believe Kabul is under "imminent threat," defense officials remain concerned.

Earlier in the day, a U.S. defense official told Fox News that Kabul could fall to the Taliban at any moment. "It could be tomorrow," the official said, "or it could be a month."  

Ultimately, the former prediction proved to be true.

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"I give the department a lot of credit for sending the very sizable force," Punaro said. "These Marine expeditionary units, these are not just straight-legged infantry soldiers, these are people that got helicopters, they got logistics support, these are full-up battle rounds."

"The practical reality is any way you look at this, this is a combat-type mission," he added.

An official told Fox News on Friday that fierce fighting had begun taking place just 30 miles outside of Kabul – heightening the security threat as U.S. soldiers looked to evacuate people through the Hamid Karzai International Airport.

Former Navy Seal turned retired-Protective Officer for the CIA's elite Global Response Staff, Jimmy Graham, told Fox News that maintaining the airport was crucial to the evacuation’s success. 

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"They have to maintain the airport," Graham said. "It’s going to take a lot of fire-power, just because you have to think about the what-ifs," Graham, who served in Benghazi shortly before and after the 2012 attack, said.  

"If you get a bunch of Taliban fighters in there, you need to be able to fight a battle to keep those lines open. You can’t lose the line to the airport," he added.

"That route must be maintained and defended if possible. It’s not a huge ride but it’s not a short ride" Graham said, reflecting on his time spent in Kabul with the CIA.

"It takes a lot of people to secure a route that’s going from an embassy to an airport because you don’t know where those chokepoints will be and if you lose any one of them, that means you just lost your access," he explained. "That means air support, that means everybody ready to fight a battle to keep that line open until that last person is out of there."

President Biden authorized the deployment of an additional 1,000 troops to be deployed to Afghanistan Saturday, after approving the deployment of 3,000 service members earlier in the week.

The 4,000 deployed soldiers joined the additional 1,000 American troops already positioned at the airport and embassy.  

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Republican lawmakers have condemned the administration’s response to the Taliban takeover of Afghanistan and GOP Sen. Joni Ernst of Iowa – the first female combat veteran elected to the Senate – accused the Pentagon of "whitewashing" the evacuation’s security implications. 

"There is every possibility of combat with the Taliban," Ernst told Fox News. "To say this is not a combat mission downplays the danger and complexity of the mission and is more whitewashing from the Biden administration of their completely bungled withdrawal."

Republican Sen. Dan Sullivan of Alaska said the administration was "playing word games."

"A security mission and a combat mission in Afghanistan at this juncture is a distinction without a difference. One could morph into the other at a moments' notice. The combat troops being sent to Afghanistan know this," Sullivan said in a statement to Fox News. 

"Instead of continuing to play word games, what the Pentagon needs to do is make sure these brave Marines and soldiers have the resources to be able to fully complete their mission which could involve combat at any moment," he added.