The airfield at the Kabul airport reopened for flight operations at 3:35 p.m. ET and the first C-17 loaded with Marines landed soon afterwards, according to Maj. Gen. Hank Taylor, the Joint Staff's director of current operations.

There are currently 2,500 American troops at the airport and Taylor said that by the end of the day there will be 3,000 to 3,500 troops on the ground.

Taylor said that 700 Afghan visa applicants have departed Kabul in the past 48 hours via commercial and charter aircraft, making it 2,000 total who have left Kabul.

"Our focus right now is to maintain security at a time, to continue to expedite flight operations while safeguarding Americans and Afghan civilians," said Taylor.

Gary Reid, who runs the DOD's Crisis Action Group for Afghanistan, confirmed that the 22,000 Afghan interpreters and their families will be housed at Fort McCoy, Wisconsin, and Fort Bliss, Texas. Other military bases may be identified as needed.

Given Monday's suspension of air operations because of the rush of civilians to the airport, Reid acknowledged that U.S. officials "anticipate picking up the pace" of flights now that the airport has reopened.

Pentagon spokesman John Kirby was matter of fact in saying that the crush of civilians at the airport came about because "there were a lot of Afghans that wanted to get out of the country."

Kirby pushed back on the notion that there "was a lack of planning" in terms or evacuation operations at the airport.

Kirby said he the expectation is that potentially 5,000 people a day could be evacuated on 20-30 flights a day if possible. He would not provide details about how Afghan SIV/civilians would be able to make their way to the airport.

Chairman of the Senate Select Committee on Intelligence Sen. Mark Warner, D-Va., said in a statement that the images coming out of Afghanistan in recent days have been devastating and that along with the heads of other relevant committees will "ask tough but necessary questions about why we weren't better prepared for a worst-case scenario involving such a swift and total collapse of the Afghan government and security forces."

"We owe those answers to the American people and to all those who served and sacrificed so much," Warner said in the statement.

First, Warner said, the focus needs to be on securing the airport in Kabul, restoring evacuation flights and allowing America's trusted Afghan partners to find safe haven outside of the country.

"At this moment, our top priorities must be the safety of American diplomats and other citizens in Afghanistan, and the extraction of Afghans who are at greatest risk, including those who bravely fought alongside our forces since 2001. The world must know that the United States stands by her friends in times of need, and this is one of those times," he said in the statement.

"We must do everything we can to secure the airport in Kabul, restore evacuation flights, and allow our trusted Afghan partners to find safe haven in the United States or elsewhere before it is too late," he continued.

-ABC News' Trish Turner

Biden also took the chance to directly address concerns that the U.S. did not begin evacuating Afghan civilians who helped aid the mission ahead of withdrawing troops.

"Part of the answer is some of the Afghans did not want to leave earlier, still hopeful for their country," Biden said. "And part of it is because the Afghan government, and its supporters, discouraged us from organizing a mass exodus to avoid triggering, as they said, a crisis of confidence."

"As we carry out this departure, we have made it clear to the Taliban if they attack our personnel or disrupt our operation, the U.S. presence will be swift and the response will be swift and forceful," Biden added, redirecting focus on the immediate goal of getting all Americans and Afghan allies who helped with the U.S. mission get out of the country safely.

"Once we have completed this mission, we will conclude our military withdrawal. We will end America's longest war after 20 long years of bloodshed," Biden said.

Following his remarks, Biden headed back to Camp David where he will continue to receive briefings on the situation, the White House said.

While Biden stood firmly by his decision to withdraw troops from Afghanistan in his afternoon remarks, he hardly addressed the chaotic evacuation efforts in Kabul and did not offer any apologies to the people of Afghanistan.

"I am president of the United States of America, and the buck stops with me. I'm deeply saddened by the facts we now face, but I do not regret my decision to end America's war fighting in Afghanistan and maintain a laser focus on our counterterrorism missions there and in other parts of the world," he said.

"I made a commitment to the brave men and women who serve this nation that I wasn't going to ask them to continue to risk their lives in a military action that should have ended long ago," Biden said, before rejecting comparisons to the Vietnam War, as his officials have done in recent days.

"Our leaders did that in Vietnam when I got here as a young man. I will not do it in Afghanistan," Biden added. "I know my decision will be criticized. But I would rather take all that criticism than pass this decision on to another president of the United States, yet another one, a fifth one."