Lawmakers in the House and Senate said Sunday they would investigate the apparent assassination attempt on former president Donald Trump, demanding documents and testimony from the U.S. Secret Service, while others moved to enhance the security provided to presidential candidates.

At the center of the maelstrom on Capitol Hill are questions posed by Republicans and Democrats alike about the agency charged with safeguarding Trump and top U.S. leaders — and how a gunman managed to open fire on someone under its protection.

House Oversight Chairman James Comer (R-Ky.) called for Secret Service Director Kimberly Cheatle to appear before the committee next week, and Mark Green (R-Tenn.), chair of the House Committee on Homeland Security, requested documents, details and a briefing pertaining to the security plan for Trump’s rally Saturday in Butler County, Pa.

In a three-page letter released Sunday, Green raised “serious concerns regarding how a shooter was able to access a rooftop within range and direct line of sight of where President Trump was speaking.”

Later, Sen. Gary Peters (D-Mich.), chairman of the Senate Homeland Security and Governmental Affairs Committee, announced a separate investigation into the shooting, which officials said left one rally attendee dead and two others injured. Trump said on social media that he was “shot with a bullet that pierced the upper part of my right ear.” The gunman, identified by the FBI as 20-year-old Thomas Matthew Crooks of Bethel Park, Pa., was killed by the Secret Service.

Peters and Homeland Security Secretary Alejandro Mayorkas were set to speak Sunday and committee staff were due to receive a briefing from the department.

The House Sergeant-at-Arms held a call with House Republicans, who were told to expect increased security at the party’s convention this week in Milwaukee, according to people familiar with the conversation. Lawmakers also were told they can request additional security in their districts.

House Speaker Mike Johnson (R-La.) opened the conversation with a call for Republicans and Democrats to lower the temperature, according to members who participated in the call. He also asked that Democrats specifically tone down their rhetoric claiming that a Trump victory in November’s election would mean the “end of democracy” or a “national emergency,” according to one member who, like some others, spoke on the condition of anonymity to discuss what was said.

Members who spoke during the call called for accountability and largely echoed concerns about the Secret Service and why the shooting was not prevented.

“It’s unthinkable, unfathomable,” House Intelligence Committee Chairman Michael R. Turner (R-Ohio) said in an interview on CNN. “We need to know: Was this a protocol failure? Was this a resources issue? Or is this just a failure of those who were on-site that day?”

Other potential investigations will be considered after the Republican convention, according to a person who was briefed on the call. Those could examine Secret Service security protocols and resources, and whether sufficient funds are dedicated to former presidents, presidential candidates and those who need protection, the person said.

President Biden, in brief remarks at the White House on Sunday, said he would also seek a review of the Secret Service’s planning ahead of the rally and its response after the shooting.

Not all members agreed with the rush to question the planning and response from the Secret Service, including Rep. Mike Kelly (R-Pa.), who witnessed the bloodshed at the rally from the front row and the response by those who whisked Trump safely off the stage.

“There’s a danger in saying these people didn’t do their jobs — when I saw them rush to rescue the president, they were doing their job,” Kelly said in a brief interview with The Washington Post. “We need to step back a little bit and let the process play out.”

Rep. Ruben Gallego (D-Ariz.), a combat veteran who sits on the House Armed Services Committee, sent a separate letter to Cheatle seeking details about the agency’s planning around the rally, including information about threat assessments, any failures in protocol and requests for additional resources. Gallego also asked whether the agency will “reconsider its denial of protection” for Robert F. Kennedy Jr., who is running for president as an Independent.

“This was a security failure at the highest level, not seen since the attempted assassination of President Reagan” in 1981, Gallego wrote. “This cannot happen, and I demand accountability.”

Reps. Ritchie Torres (D-N.Y.) and Michael Lawler (R-N.Y.) introduced a bill on Sunday that similarly proposed enhanced protection for all major presidential candidates.

“Anything less would be a disservice to our democracy,” they said in a joint statement.

Abigail Hauslohner contributed to this report.