Thousands of prisoners freed by Taliban could pose threat to U.S.

State of play: U.S. forces handed control of the airfield to Afghan government forces in early July.

• Estimates suggest that from 5,000 to 7,000 prisoners were left behind following the U.S. withdrawal, per CNN.

The big picture: The prison, Pul-e-Charkhi, is the largest in Afghanistan and contained a maximum-security cell block for al Qaeda and Taliban prisoners.

• Afghan government troops surrendered control of the base, located on the outskirts of Kabul, to the Taliban without a fight.

The big picture: U.S. Chairman of the Joint Chiefs of Staff Mark Milley told senators Sunday that a previous assessment of how soon terrorist groups will likely reconstitute in Afghanistan will speed up because of what's happening there now, three sources on the phone call told Axios.

• On the phone call between top Biden officials and senators from both parties, Sen. Lindsey Graham (R-S.C.) asked Defense Secretary Lloyd Austin and Milley whether, in light of recent events, they will revise an assessment to Congress in June of a "medium" risk of terrorist groups reconstituting in Afghanistan within two years.

• Milley responded "yes" — that he would have to assume that timeline would get moved up and that he would be happy to brief senators in a classified setting.

Go deeper: Scoop: Joint Chiefs chairman moves up terrorist threat in Afghanistan.