Kimberly Cheatle, director of the U.S. Secret Service, acknowledged Monday that the near-assassination of former President Donald Trump represented a fundamental failure on her agency’s part, but refused to explain exactly what went wrong.

Speaking before lawmakers on Capitol Hill, Cheatle described the July 13 shooting of Trump and attendees at his rally in Butler, Pennsylvania, as “the most significant operational failure” at the Secret Service in decades.

“The Secret Service’s solemn mission is to protect our nation’s leaders,” Cheatle said in an opening statement before the House oversight committee. “On July 13th, we failed.”

Cheatle said she took “full responsibility for any security lapse” by her agency, though she has rebuffed calls for her resignation from oversight chair Rep. James Comer (R-Ky.) and other Republicans.

And for the most part, Cheatle refused to answer specific questions about the Secret Service’s planning for the 13th, instead speaking in generalities about how the agency operates. Cheatle said she would defer to the multiple ongoing investigations of the failure, including the FBI’s criminal investigation into the shooting.