Secret Service Director Kimberly Cheatle tells House Trump shooting was 'most significant operational failure' in decades

July 22 (UPI) -- Secret Service Director Kimberly Cheatle on Monday was on Capitol Hill to face lawmakers as some have called for her resignation in the wake of the assassination attempt against former President Donald Trump in Pennsylvania.

The assassination attempt at Trump's campaign rally in Butler, Pa., was characterized as "the most significant operational failure of the Secret Service in decades," Cheatle told House Oversight and Accountability Committee members.

"On July 13, we failed," Cheatle said Monday morning in her opening statement as she took "full responsibility for any security lapses in our agency."

"As an agency, we are fully cooperating with the FBI's investigation, the oversight you have initiated here, and conducting our own internal mission assurance review at my direction," Cheatle wrote in remarks obtained by ABC News prior to Monday's hearing. "Likewise, we will cooperate with the pending external review and the DHS Office of the Inspector General."

On Monday she expressed her condolences to the families of the former president and Corey Comperatore, a former Pennsylvania firefighter who was shot and killed at the Butler campaign rally.

"I will move heaven and Earth to ensure another incident like July 13 does not happen again," Cheatle, who has rejected calls for her to resign, said Monday.

Security for the Republican presidential nominee, she said, "has been steadily increasing as threats evolve" but claimed it already had been increasing even before the shooting.

"Looks like you guys were cutting corners," Rep. Jim Jordan , R-Ohio, claimed Monday as he grilled Cheatle during a rapid series of questions about who she spoke to at the White House regarding Secret Service efforts on July 13.

The federal agency protects at least 36 individuals on a daily basis as well as visiting world leaders, such as Israeli Prime Minister Benjamin Netanyahu who arrived Monday in Washington, Cheatle says.

"Our agency needs to be adequately resourced," she told committee members. However, the Secret Service, she said, "is not political."

Claims were made that the Secret Service had previously denied extra requests for security as multiple federal agencies now are in the middle of their own investigations to see more clearly what security measures failed that day.

The Secret Service, a federal law enforcement agency under the Homeland Security Department, has an annual $3.1 billion budget, Rep. Jim Comer, R-Ky., House Oversight Committee chairman, pointed out as Cheatle finished her opening statement.

The AR-15-style weapon used to shoot at Trump was legally purchased by 20-year-old shooter Thomas Crooks' father. The committee's ranking Democrat, Rep. Jamie Raskin of Maryland, said he believes most American citizens are uncomfortable with how easily accessible that type of weapon is.

Cheatle said the assets that were requested by other agencies tasked with aiding to protect Trump on July 13 "were given" by the Secret Service, but pushed back on claims her agency was not fully prepared for the campaign event on the day of the shooting.

"There were no assets denied for Butler on the 13th," she said. Trump, on his part, has laid praise on the "very brave Secret Service agents" who "rushed to the stage" to protect him and quickly killed the shooter.

House Speaker Mike Johnson , R-La., last week in Milwaukee at the Republican National Convention said he would call for Cheatle's ouster. He joins a growing list of Republicans, including Senate Minority Leader Mitch McConnell , R-Ky., and House Majority Leader Steve Scalise , R-La., who have called on her to resign.

She also was confronted by Republican senators at the Republican National Convention last week, who recorded and shared video of them calling for her to answer questions about the shooting

On Saturday, Rep. Brendan Boyle, D-Pa., became the first Democrat to call for Cheatle to step down.

"The evidence coming to light has shown unacceptable operational failures," Boyle previously said. "I have no confidence in the leadership of the United States Secret Service if Director Cheatle chooses to remain in her position."