A multifaceted terrorist attack in Kabul killed 13 U.S. military service members and injured 15 more, stoking congressional fears that the evacuation of American citizens and Afghans who worked with the United States will collapse on a timetable dictated by terrorists.

“The ones who are gonna be really harmed by this are gonna be the [special issuance visa holders] — those Afghans who have not gotten out yet,” a Senate Republican aide said Thursday. “I think that window has really closed for them.”