Secret Service Director Kim Cheatle told the House Oversight Committee on Monday that the assassination attempt was "the most significant operational failure at the Secret Service in decades."

"There are multiple ongoing investigations into this incident, hundreds of people to interview, and thousands of documents to review. I do not want to inadvertently provide you today with inaccurate information," she said. "I may not be able to speak specifically to certain items that have circulated over the past nine days."

Cheatle said 36 people are currently under Secret Service protection, including Israeli Prime Minister Benjamin Netanyahu, who arrives in the U.S. on Monday.

"Immediately following the assassination attempt, I directed the activation of my Crisis Center and assembled my executive team to begin surging more protective resources to the former president and to ensure the wellness of our people post-incident, all while securing an active crime scene," she said.

Cheatle said she is not blaming state and local partners and said planning for the event began 10 days before the rally.

"The level of security provided for the former president increased well before the campaign and has been steadily increasing as threats evolve," she said. "The security plan included a full assessment of the Butler Farm show grounds to identify security vulnerabilities and craft a security plan for our protectee, attendees and the public."

-ABC News’ Luke Barr

House Oversight Committee Chairman James Comer, R-Ky., said the assassination attempt against former President Donald Trump was "preventable," and said the committee is "concerned the Secret Service lacks the management to keep protectees safe."

"A former president and current candidate for president was shot in the head by a sniper within 500 feet of the podium," Comer said in his opening statement ahead of Secret Service Director Kim Cheadle’s testimony on Monday. "This is unacceptable. We are concerned the Secret Service lacks the proper management to keep protectees safe from bad actors. Americans demand answers, but they have not been getting them from the Secret Service. We are instead learning about the events surrounding the assassination attempt from whistleblowers and leaks. Americans demand accountability, but no one is yet to be fired for this historic failure."

Comer reiterated his call for Cheatle to resign.

Ranking committee member Jamie Raskin, D-Md., said it is Congress' responsibility to learn from the attempted assassination and to ask tough questions of the director as to how this could have happened.

"Some are calling it a miracle that former President Trump escaped this AR-15 attack, unlike so many thousands of our fellow citizens who have been killed or seriously committed in other AR-15 shootings," Raskin said. "Our job in Congress is not simply to marvel at miracles ... but to act as public policy legislators to do whatever we can to prevent future political violence, attempted assassinations and massacres."

Raskin said he and Comer are "determined to get the bottom" of the "stunning security failures."

He also called on Congress to ban assault weapons, noting that the gunman who shot Trump was 20 years old and used his father’s AR-15.

-ABC News’ Luke Barr

House Homeland Security Committee Chairman Mark Green, R-Tenn., is calling on Secret Service Director Kim Cheatle to resign.

"Cheatle argued the Secret Service could not position counter-snipers in the location of the shooter because of the angle of the roof. This was an absurd, unacceptable, and obviously unfounded excuse," he said in a statement. "Cheatle placed blame at the feet of local law enforcement for the failures of that day -- blatantly ignoring the fact that local officers indicated ahead of time they did not have the ability to secure the building that the shooter used to fire those fateful shots."

"Director Cheatle has rightfully admitted the near assassination of a former president was a failure. She even said the buck stops with her," Green continued. "For the good of this country, Director Cheatle must resign immediately."

Green will visit the shooting site in Butler, Pennsylvania, at 11:30 a.m. ET Monday with a bipartisan group of members on the House Homeland Security Committee.

House Republicans are expected to hold a vote later this week on creating a task force to investigate the attempted assassination of former President Donald Trump.

The resolution, entitled "Establishing the Task Force on the Attempted Assassination of Donald J. Trump," will be introduced by Pennsylvania Republican Rep. Mike Kelly – who represents Butler, Pennsylvania, where the Trump rally took place.

The task force will include six Republicans and five Democrats and issue its findings to the House no later than Dec. 13, 2024.

-ABC News' Lauren Peller