The United States Secret Service director told Congress on Monday that the attempted assassination against former President Donald Trump was the "most significant operational failure at the Secret Service in decades" and took full responsibility for the lapses in security that day.

"The Secret Service's solemn mission is to protect our nation's leaders. On July 13, we failed," Secret Service Director Kim Cheatle testified before the House Committee. "As the director of the United States Secret Service, I take full responsibility for any security lapse. We are fully cooperating with ongoing investigations. We must learn what happened."

In her first hearing before Congress, which lasted for 4 hours and 40 minutes, Cheatle also told the committee that she will move "heaven and Earth" to ensure that what occurred will never happen again.

"Our mission is not political. It is literally a matter of life and death, as the tragic events on July 13 remind us of that," she said. "I have full confidence in the men and women of the Secret Service. They are worthy of our support in executing our protective mission."

This is yet another consequential week for the Secret Service, which is tasked with providing security to Israeli Prime Minister Benjamin Netanyahu during his visit to Washington, D.C. -- something the director has been focused on while also overseeing the security for the Republican National Convention in Milwaukee last week.

Cheatle faced a grilling before the House Oversight Committee over how her agency handled security around the attempted assassination of Trump.

Cheatle faces calls to resign

She has faced calls from multiple Republicans and Democrats to resign after the former president was targeted at his rally in Butler, Pennsylvania. Rep. John Comer, R-Ky., chairman of the House Oversight Committee, told Cheatle in his opening statement that he is among those who believe she should resign.

By the end of the hearing, Rep. Jamie Raskin, D-Md., the ranking member of the committee, joined in the calls for Cheatle to resign, saying that the director "has lost the confidence of Congress at a very urgent and tender moment in the history of the country and we need to quickly move beyond this." Following the hearing, Raskin joined Comer in sending Cheatle a letter requesting her resignation.

"I believe, Director Cheatle, that you should resign," Rep. Ro Khanna, D-Calif., also told Chatle during the hearing. Khanna added that his colleagues on both sides of the aisle want her to step down.

"I hope you'll consider it," Khanna said.

Referring to an interview Cheatle had with ABC News two days after the assassination attempt, Comer told Cheatle, "You answered more questions with an ABC reporter than you have with members of Congress."

Cheatle has said she will not resign.

Rep. Marjorie Taylor Greene, R-Ga., asked if the director brought a timeline of the incident to the hearing. Cheatle responded that while she has a timeline, "it doesn't have specifics."

"That's shocking," Green said in response. "That is absolutely unacceptable. That means you're a failure at your job."

Cheatle asked about why no agent was placed on roof the gunman fired from

The Secret Service director was asked Monday about her statements in an interview with ABC News about why no agents were placed on the roof of a building outside the security perimeter of the rally, where the suspected shooter fired from, because of the roof's sloping nature.

Cheatle said Monday that there was "overwatch" provided for the roof, but she did not elaborate.

"I should have been more clear in my answer when I spoke about where we placed personnel in that interview. What I can tell you is that there was a plan in place to provide overwatch, and we are still looking into responsibilities and who was going to provide overwatch, but the Secret Service in general, not speaking specifically to this incident, when we are providing overwatch, whether that be through counter-snipers or other technology, prefer to have sterile rooftops," Cheatle said.

Cheatle also admitted that the FBI has told her the shooter flew a drone over the rally site, but she did not go into more details.

Why was Trump allowed on stage while there was a threat?

Cheatle said that if the detail had information that there was a threat to the former president, they wouldn't have brought Trump on stage, but she said the information wasn't passed along to them.

"If the detail had been passed information that there was a threat, the detail would never have brought the former president out onto the stage," she said. "That is what we do. That is who we are. We are charged with protecting all of our protectees. Distinguish between someone who is suspicious and someone who's threatening. A number of times, protective events where suspicious people are identified, those individuals have to be investigated and determine what is it that identifies that person as suspicious."

She said the Secret Service did not know the suspect had a weapon before former President Trump took the stage.

'Clearly a breakdown'

Cheatle said she has read the intelligence regarding the threat from Iran against former President Trump. The Iranians have long pledged retribution against Trump and members of his administration for the killing of Iranian military officer Qasem Soleimani in January 2020.

Rep. Mike Turner, R-Ohio, who is the chairman of the House Intelligence Committee, said that when FBI Director Christopher Wray briefed congressional members, he was "incensed" that this threat information was not taken into account when planning for the rally.

"There was clearly a breakdown or a failure that day," Cheatle said.

Cheatle also said that no personnel or assets were denied to Trump at the Butler rally.

But Cheatle was also grilled about whether her agency denied Trump's security detail resources it requested in the two years before Saturday, as first reported by The Washington Post, something her agency initially denied but then admitted over the weekend.

In a statement to ABC News, Secret Service spokesperson Anthony Guglielmi said, "In some instances where specific Secret Service specialized units or resources were not provided, the agency made modifications to ensure the security of the protectee. This may include utilizing state or local partners to provide specialized functions or otherwise identifying alternatives to reduce public exposure of a protected."

"For the event in Butler, there were no requests that were denied," she said.

Cheatle praised the agents guarding Trump for putting their lives on the line to protect him with their bodies even as shots were still being fired in their direction. She said that in less than three seconds, agents from Trump's detail threw themselves onto the former president and helped to secure him.

"I would grade the agents and officers who selflessly threw themselves in front of the president and neutralized the threat an A. I think that we need to examine the events that led up to and prior to that day," she said.

One shot took out gunman

Cheatle said there was one shot that took out the suspect from the Secret Service counter-sniper, whom she has spoken to since the assassination attempt.

Cheatle said she is "committed" to finding answers and has taken accountability and "will continue" to take accountability.

"I think that I'm the best person to lead the Secret Service at this time," Cheatle said, touting her increase in hiring and staffing since her tenure as head of the agency began in 2022.

She also said that if someone needs to be held accountable, she will do that.

"I've been a Secret Service agent for nearly 30 years. I have led with integrity, and I follow our core values of duty, justice, honor, loyalty and courage, and I am doing that in this case, and I assure this committee that I will provide answers when we have a full and complete report, in addition to cooperating with all of the other investigations that are ongoing," Cheatle said.

Multiple members of the committee expressed frustration that Cheatle declined to answer many of their questions, with the director saying that "the facts of this particular event are still unfolding" and that it's been just nine days since the assassination attempt.

Rep. Alexandria Ocasio-Cortez, D-N.Y., pressed Cheatle for answers despite Cheatle saying the final report on the assassination attempt won't be finalized for another 60 days.

"This is about the safety of some of the most highly targeted and valued targets internationally and domestically in the United States of America," Ocasio-Cortez told Cheatle. "So the idea that a report will be finalized in 60 days, let alone prior to any actionable decisions that would be made, is simply not acceptable. It has been 10 days since an assassination attempt on a former president of the United States, regardless of party, there needs to be answers."

Ocasio-Cortez said Congress is "flying blind" on any legislation they might want to enact as a result of the attempt on Trump's life.

House Speaker Johnson in attendance

The hearing room on Monday was packed, with standing room only, as opening statements were given by Comer, Raskin and Cheatle. House Speaker Mike Johnson was also in attendance.

Before the hearing started, Johnson briefly met with Cheatle and told her to resign, a senior GOP leadership aide told ABC News.

In a rare bipartisan statement, Raskin had joined Comer in demanding that Cheatle testify after the Department of Homeland Security asked that her appearance be delayed, resulting in Comer issuing a subpoena.

The DHS inspector general has opened three separate investigations into what went wrong. The FBI is currently leading a criminal investigation, and Johnson has pledged congressional resources for a separate investigation.

As the head of the agency, Cheatle said it was her responsibility to investigate what went wrong and ensure that it does not happen again.

"The buck stops with me," she told ABC News Chief Justice Correspondent Pierre Thomas in an exclusive interview on July 15. "I am the director of the Secret Service, and I need to make sure that we are performing a review and that we are giving resources to our personnel as necessary."

Cheatle was in Milwaukee last week overseeing security for the Republican National Convention and met with the former president on Tuesday, according to a source familiar with the situation.

"Secret Service is not political," she told ABC News. "Security is not political. People's safety is not political. And that's what we're focused on as an agency."

Republicans also signaled they would question Cheatle about past statements that promoting diversity in the agency was a top priority.

The DHS pushed back against criticism of women in Trump's security detail.

"In the days following the attempted assassination of former President Trump, some people have made public statements questioning the presence of women in law enforcement, including in the United States Secret Service," DHS Secretary Alejandro Mayorkas and other senior leaders wrote in a statement. "These assertions are baseless and insulting."

ABC News' Bill Hutchinson, Lauren Peller and John Parkinson contributed to this report.