Lawmakers are alarmed at how the would-be-assassin was able to open fire from a rooftop within 150 meters (164 yards) of the former president. President Joe Biden has also directed an independent review of the security at the rally.

A look at some of the action Monday as lawmakers sought to ensure that their panels would play a leading role in the various follow-up investigations.

House panel lines up first hearing

The first hearing about the shooting has been scheduled for next Monday, July 22, with the director of the U.S. Secret Service, Kimberly Cheatle. She'll testify before the House Committee on Oversight and Accountability.

"The United States Secret Service has a no-fail mission, yet it failed on Saturday when a madman attempted to assassinate President Trump, killed an innocent victim, and harmed others," said Rep. James Comer, the committee's Republican chairman.

Comer said lawmakers were grateful to the Secret Service agents who acted quickly to protect Trump, "but questions remain about how a rooftop within proximity to President Trump was left unsecure."

Comer's panel isn't the only House committee taking action.

The chairman of the House Committee on Homeland Security, Rep. Mark Green, R-Tenn., sent a letter to Homeland Security Secretary Alejandro Mayorkas demanding that he provide the plan to secure the perimeter of the event site, any communications about adding to Trump's security detail, and materials used to brief President Biden about the assassination attempt.

"The seriousness of this security failure and chilling moment in our nation's history cannot be understated," Green wrote in his letter, which includes a request of a briefing for committee members no later than July 22.

Senate committees weigh in

The leaders of the Senate Homeland Security and Government Affairs Committee announced Monday they will also conduct an investigation.

First, they are requesting a briefing from the U.S. Secret Service, the Department of Homeland Security, and the Federal Bureau of Investigation. That will be followed by a public hearing as well as requests for documents.

In a letter to Mayorkas and FBI Director Christopher Wray, senators said they want to understand how the shooter was able to get so close to Trump and what steps the department is taking to "increase its protection of presidential candidates and ensure the safety of the election."

Lawmakers also want to know what additional security requests have been made by Trump's campaign or protective team since Nov. 15, 2022.

Sen. Gary Peters, the Democratic chairman of the committee, and Rand Paul, the ranking Republican,, said the briefing for members should happen before July 25, while a hearing will be sought as soon as possible, but no later than August 1.

"This committee has an obligation to unearth the truth about the failures on Saturday and before, no matter how inconvenient to the government," Paul said. "We will leave no stone unturned."

Committee members also sought to emphasize the investigation would be bipartisan, as lawmakers from both parties called for it.

"As we move forward, we need to come together as Americans, reject baseless conspiracy theories on both sides, and focus on a fact-based effort to get all available information and ensure accountability so that this never happens again," said Sen. Jacky Rosen, D-Nev.

Meanwhile, Republicans on the Senate Judiciary Committee wrote to the panel's chairman, Sen. Dick Durbin, D-Ill., seeking a hearing with Cheatle, Mayorkas and Wray as witnesses.

"Our hearts are broken and our prayers are with those murdered and injured by this senseless violence," the Republicans wrote. "Chair Durbin, we hope to work with you to investigate this matter publicly, and to bring answers and confidence in our system to the American people."