Chairman of the Joint Chiefs of Staff Mark Milley told senators on 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, according to three sources on the phone call.

Why this matters: Protecting the U.S. against terrorist threats to the homeland was an original reason for engaging the U.S. in this 20-year war.

• Afghanistan has fallen to the Taliban much faster than President Biden or his top military leaders predicted.

Behind the scenes: On a Sunday phone call between top Biden officials and senators from both parties, Sen. Lindsey Graham (R-SC) asked Defense Sec. 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 that timeline would get moved up, and that he would be happy to brief senators in a classified setting.

This is a developing story... more to come