(CNN) — When United States Secret Service Director Kimberly Cheatle appears Monday in front of the House Oversight Committee – alone and under subpoena – she will be forced to provide many answers to what is essentially a single question: How did the Secret Service’s biggest failure in four decades happen under her watch?

In the days following the attempted assassination of former President Donald Trump, Cheatle has done no press conferences and very few interviews. Monday’s hearing will mark the first opportunity for a lengthy dive into the security failures at Trump’s July 13 rally.

“The Secret Service’s solemn mission is to protect our nation’s leaders. On July 13th, we failed,” the director is expected to tell lawmakers, according to prepared remarks reviewed by CNN. “As the Director of the United States Secret Service, I take full responsibility for any security lapse.”

The agency, Cheatle is expected to say, “must learn what happened and I will move heaven and earth to ensure an incident like July 13th does not happen again. Thinking about what we should have done differently is never far from my thoughts.”

House Oversight Chairman James Comer on Sunday promised the hearing would be extensive and detailed.

Cheatle is “going to have about a six-hour hearing, and she’s going to have hundreds of questions that she’s going to have to answer,” Comer said on “Fox News Sunday.”

In his opening statement Monday, released prior to the hearing, Comer said Cheatle should resign and noted that so far, she has refused to do so.

“The Secret Service has a zero fail mission, but it failed on July 13 and in the days leading up to the rally,” Comer’s opening statement says. “The bottom line is that under Director Cheatle’s leadership, we question whether anyone is safe. Not President Biden, not the First Lady, not the White House, not presidential candidates.”

In the week since the rally in Butler, Pennsylvania, relatively little has come out about the shooter’s motive, how he was able to perch on a nearby rooftop with an AR-style weapon and why Trump’s team wasn’t warned about a potential threat.

Republican lawmakers in particular have been upset with the lack of answers, and many have called for Cheatle’s resignation.

Cheatle has said that “the buck stops with me,” but there has also been finger pointing between the Secret Service and local law enforcement over who had responsibility for what and whether all the resources needed were present.

She is expected to say in her remarks Monday that the agency’s mission “is not political.”

“It is literally a matter of life and death, as the tragic events on July 13th remind us. I have full confidence in the men and women of the Secret Service. They are worthy of our support in executing our protective mission.”

Here’s what to watch for:

Why wasn’t Trump’s team told of a potential threat?

The shooter, Thomas Matthew Crooks, was spotted multiple times with a rangefinder, a hunting device similar to a pair of binoculars that calculates distance, prior to the shooting. Further, police had circulated a photo of him they had taken.

A source told CNN that about 19 minutes before the shooting occurred, law enforcement was trying to locate Crooks, but they could not find him until he was on the roof.

Butler Township Manager Tom Knights told CNN police responded to a call of a “suspicious male” around the same time that Trump arrived for his Pennsylvania rally on Saturday – at least ten minutes before he took the stage for his speech.

However, members of Trump’s team weren’t told that law enforcement was trying to locate Crooks as they were preparing the former president to take the stage.

There was also no conversation about whether Trump should have delayed his entrance, according to sources who were with him at the rally.

“We would have never let him go out there if we thought there was a threat to him,” one source present with Trump told CNN.

A Secret Service source familiar with the incident told CNN that Crooks had been “deemed a suspicious person, but that doesn’t necessarily mean that there was any indication that he was an immediate threat” or had a weapon until just before the shooting.

Suspicious people aren’t uncommon at events like Trump rallies – even on Saturday, “a guy tried to come in with a goat” and a woman showed up “riding a horse with a giant Trump flag,” and both were also deemed suspicious, the Secret Service source said.

Why wasn’t the roof secured?

Crooks fired several shots at Trump from a roof roughly 150 yards away from Trump’s podium. He fired from the roof of a building that was also occupied by a local sniper team on the second floor and served as a staging area for tactical support teams at the rally.

Cheatle told ABC News last week that a sniper team was not positioned on the roof of the building due to its slope.

“That building in particular has a sloped roof, at its highest point,” Cheatle told ABC News. “And so, there’s a safety factor that would be considered there that we wouldn’t want to put somebody up on a sloped roof. And so, the decision was made to secure the building, from inside.”

If the slope of the roof didn’t stop the shooter’s ability to open fire, why did it stop law enforcement from staging there? Secret Service snipers, including the ones who killed Crooks, were also staged on a rooftop with a much steeper incline without a problem.

Despite its location, the building also wasn’t in the security perimeter.

In an interview with CNN, Cheatle said the perimeter “encompassed the area that we needed to secure the event that we had on that day.”

A senior law enforcement official told CNN on Saturday that the Secret Service did not have drone support at the rally, though it does have drone capabilities generally. The source said the agency utilized counter-sniper teams in place of drones.

Were assets rejected?

Trump’s security detail had complained it was not being given enough resources and personnel by the Secret Service over the past two years, something the agency acknowledged this weekend.

A spokesperson for the Secret Service said in a statement Saturday that the agency has not provided certain resources in the past but has instead provided other security measures including from local partners.

A Secret Service official told CNN that examples of these changes included having local sniper teams in place when the Secret Service could not provide its own or having hand-held magnetometers and other measures established at certain events where larger, walk-through magnetometers weren’t available.

Meanwhile, the nature of an alleged Iranian plot to kill Trump also became known last week. And while there is no evidence connecting it to the shooter, it raises the question about the level of security at Trump events.

Asked whether the Secret Service had increased the security it provides to the former president as a result, the director said, “We have been doing that over a series of several months, to include on that day.”

Cheatle would not, however, say whether all elements of the former president’s detail were increased as a result of the threat from Iran.

What was the motive?

Cheatle will be under pressure from lawmakers to deliver more about the motive behind the shooting.

The emerging profile of Crooks more than a week after the shooting has left authorities puzzled about a motive for his assault. Investigators are speculating that his intentions may have been less politically motivated and more about attacking the highest-profile target near him.

The investigation remains in its early stages, officials caution. Still, in some ways, Crooks seems similar to the dozens of other young men who’ve wreaked havoc across the US with high-powered assault-style rifles in recent years. He had few close friends, he would often go shooting at a local firing range, and he didn’t seem to display strongly held views that would suggest a politically driven assassination, according to CNN interviews with law enforcement and a review of notes from a briefing to Congress.

At the same time, it has been discovered that he visited the rally site twice after it was announced and may have even flown a drone over the area on the day of the shooting.

How much longer will Cheatle remain director?

Cheatle is a nearly three-decade veteran of the Secret Service, serving in various field offices and vice presidential details including then-Vice President Joe Biden’s detail. Cheatle left the Secret Service in 2021 as the Assistant Director of the Office of Protective Operations – a role she held when the Secret Service scrambled to protect then-Vice President Mike Pence from rioters on January 6, 2021.

Multiple Republican lawmakers, including House Speaker Mike Johnson, have called on Cheatle to resign.

“I don’t understand her decision-making process, and I don’t think she’s fit to lead at this critical time,” House Speaker Mike Johnson told Fox News last week.

Rep. Brendan Boyle, a Pennsylvania Democrat, also said Cheatle needs to leave.

“I’m very sorry to reach this conclusion: I have no confidence in the leadership of the United States Secret Service. I hereby call on Kimberly Cheatle to resign,” Boyle said on X.

This story has been updated with additional comments.

CNN’s Evan Perez, Kristen Holmes, Holmes Lybrand and Aileen Graef contributed to this report.