Members of Congress from both parties announced plans Monday to investigate how a shooter was able to get within striking distance of former President Donald Trump, demanding answers from the authorities responsible for protecting the Republican nominee for president.

The attempted assassination, which amounts to the most serious attempt to kill a U.S. president or presidential candidate in more than 40 years, sparked a string of questions and outrage from lawmakers.

Senate Homeland Security and Governmental Affairs Chairman Gary Peters, D-Mich., and ranking member Rand Paul, R-Ky., on Monday announced the panel would conduct a bipartisan investigation. They also plan to hold a hearing.

Peters said the panel is focused on getting all the facts about the “security failures that allowed the attacker to carry out this heinous act of violence.”

And House Oversight and Accountability Chairman James R. Comer, R-Ky., announced that Secret Service Director Kimberly Cheatle would appear before the panel July 22 for a hearing on the assassination attempt.

“Questions remain about how a rooftop within proximity to President Trump was left unsecure,” Comer said. “Americans demand answers from Director Kimberly Cheatle about these security lapses and how we can prevent this from happening again.”

Speaker Mike Johnson, in an interview with the “Today” show on Sunday, said Congress will do a full investigation “to determine where there were lapses in security and anything else that the American people need to know.”

The Secret Service said a shooter fired multiple shots toward the stage from an “elevated position,” which was located outside of the rally venue. The Louisiana Republican questioned how the assailant was not noticed by Secret Service.

“Lots more questions than answers this morning,” Johnson said on Sunday.

Johnson said he spoke with Homeland Security Secretary Alejandro Mayorkas Saturday night and asked him some “pointed questions” about homeland security.

Mayorkas told reporters Monday at the White House press briefing that Secret Service had enhanced protections for Trump. “Personnel and other protective resources, technology and capabilities have been added,” Mayorkas said.

Mayorkas also said that President Joe Biden directed him to work with Secret Service to provide protection for Robert F. Kennedy Jr., an independent candidate in the 2024 presidential contest.

Rep. Jeff Duncan, R-S.C., called for an independent commission to look at the former president’s protection, saying lawmakers cannot just rely on congressional hearings or agency inspectors general to get answers on the failures to adequately protect Trump.

“The first question Americans deserve an answer to is how a rooftop with line-of-sight to the stage and podium was left un-patrolled or un-covered by kinetic surveillance,” Duncan wrote.

Sen. Lindsey Graham of South Carolina, the top Republican on the Senate Judiciary Committee, and other GOP senators wrote a letter Monday to Chair Richard J. Durbin asking for a panel hearing into the circumstances that led to the assassination attempt.

The group of Republican lawmakers asked that Durbin invite Cheatle, Mayorkas and FBI Director Christopher Wray as witnesses.

A Senate Judiciary Committee spokesperson said Durbin has asked for a closed-door briefing for committee members for next week with the Secret Service, the Department of Homeland Security and the FBI.

Durbin’s staff initiated talks over the weekend with Graham’s staff about the briefing and “other possible next steps, including a hearing,” the spokesperson said.

Meanwhile, Biden said he’s directed an “independent review” of national security at the rally and pledged to share the results with the public.

House Homeland Security Chairman Mark E. Green on Sunday sent a letter to Mayorkas requesting documents on the plan to secure the perimeter of the rally location.

The Tennessee Republican also requested documents to explain the Secret Service’s rules of engagement and records to explain the coordination between the Secret Service and state and local law enforcement.

“The seriousness of this security failure and chilling moment in our nation’s history cannot be understated,” Green wrote. “No assassination attempt has come so close to taking the life of a president or presidential candidate since President Reagan was shot in 1981. Had the bullet’s trajectory been slightly different, the assassination attempt on President Trump might have succeeded.”

Rep. Ruben Gallego, D-Ariz., wrote a letter to the Secret Service calling on the officials responsible for the planning and execution of the security plan to testify before Congress.

Gallego said the shooting raises “grave concerns” about the security measures, or lack of, taken to protect Trump.

“This was a security failure at the highest level, not seen since the attempted assassination of President Reagan. This cannot happen, and I demand accountability,” Gallego wrote.

House Intelligence Chairman Michael R. Turner, R-Ohio, in an interview with CNN, questioned how the assailant was able to get on a roof.

Turner said Congress has a role to play in the aftermath of the assassination attempt. “Both the resources that are utilized and the protocols that are utilized, we have oversight, scrutiny and responsibility for,” Turner said.

Cheatle, the director of the Secret Service, released a statement about how the agency has been working with the federal, state and local agencies to understand what happened “and how we can prevent an incident like this from ever taking place again.”

“We understand the importance of the independent review announced by President Biden yesterday and will participate fully. We will also work with the appropriate Congressional committees on any oversight action,” Cheatle said.

The Capitol Police released a statement Monday that the agency has already been operating in a heightened threat environment for months because of threats to members of Congress.

“We have been working with our federal, state and local partners on a comprehensive security plan to protect the Members of Congress during both political conventions,” the Capitol Police said. “Our officers, agents and civilians support staff remain focused on that critical mission.”

A House Administration Committee staffer confirmed that more than 200 senior Democratic staff members attended a briefing Sunday night on safety at member events in districts. Speakers included House Sergeant at Arms William McFarland and Assistant Chief of Police for Standards and Training Operations Jason Bell.

Justin Papp contributed to this report.