Progressive Rep. Ro Khanna, D-Calif., called on Secret Service Director Kimberly Cheatle to resign on Monday.

Khanna made the statement during Cheatle's testimony before the House Oversight Committee. The lawmaker grilled Cheatle over the Secret Service's failure to protect former President Trump, resulting in an shocking back-and-forth.

"Director Cheatle, would you agree that this is the most serious security lapse since President Reagan was shot in 1981?" Khanna asked.

"Yes sir, I would," Cheatle responded.

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Kimberly Cheatle testifies before the House Oversight and Accountability Committee

Progressive Rep. Ro Khanna, D-Calif., called on Secret Service Director Kimberly Cheatle to resign on Monday. (REUTERS/Kevin Mohatt)

"Well, do you know what Stuart Knight did – he was in charge, at the time, of the Secret Service – do you know what he did?" Khanna asked.

"He remained on duty," Cheatle said.

"He resigned. He resigned," Khanna corrected. "And Stuart Knight was not a Democratic appointee…. I'm not questioning your judgment, I just don't think this is partisan. If you have an assassination attempt on a president or a former president or a candidate, you need to resign."

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"That's what Stuart Knight did. He was a Republican appointee, and he took responsibility.… You cannot go leading a security agency when there's an assassination attempt on a presidential candidate," he finished.

Ro Khanna at House hearing

Rep. Ro Khanna, D-Calif., grilled Secret Service Director Kimberly Cheatle on her agency's failure to protect former President Trump. (Office of Rep. Ro Khanna)

President Reagan was shot in March 1981, and Knight resigned on Nov. 30, though his resignation was announced months ahead of time.

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Khanna is among several lawmakers who have called on Cheatle to resign. She has so far refused. Cheatle nevertheless admitted the agency "failed" in her opening statement on Monday.

Kimberly Cheatle during a House Oversight and Accountability Committee hearing

Rep. Ro Khanna is among several lawmakers who have called on Secret Service Director Kimberly Cheatle to resign. (Tierney L. Cross/Bloomberg via Getty Images)

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"The Secret Service's solemn mission is to protect our nation's leaders. On July 13, we failed," Cheatle said in her opening statement. "As director of the United States Secret Service, I take full responsibility for any security lapse of our agency. We are fully cooperating with ongoing investigations. We must learn what happened, and I will move heaven and earth to ensure that an incident like July 13th does not happen again."