(NewsNation) — A congressional source tells NewsNation the man who shot at former President Donald Trump during his rally in Butler, Pennsylvania, visited the site a few days in advance to scope it out.

Punchbowl News was first to report the news, which the source confirmed to NewsNaton.

New details have begun to come out about the heavily criticized security response to Saturday’s assassination attempt on Trump, which authorities say was carried out by 20-year-old Thomas Matthew Crooks.

At a call with senators Wednesday, the FBI and Secret Service said Crooks was identified as a possible threat over an hour before he committed the act. Twenty minutes before, he had been spotted by law enforcement looking through a range finder, which hunters often use to measure distance.

Crooks also brought multiple loaded magazines, with investigators finding a bulletproof vest and explosive in his car. He used encrypted communications that he searched online to study bullet trajectory, the source said.

Several reports state that the shooter searched for images of both Trump and current President Joe Biden, as well as the former’s events and the Democratic National Convention.

Authorities have not determined a motive for the shooting yet, which killed one man, 50-year-old Corey Comperatore, a former fire chief. 

Growing calls for Secret Service director to step down

NewsNation partner The Hill writes that senators voiced displeasure with how the call with FBI and Secret Service went, with Sen. Rick Scott, R-Fla., urging both entities to hold daily briefings as their investigations continued.

“The security of our Republic is being questioned. The Biden administration can’t wait until the investigation is complete to release details. It needs to start today,” Scott said in a statement.

GOP Sen. Ron Johnson of Florida described the briefing as “unbelievably uninformative.”

“Only 4 questions were allowed. The rest of us are supposed to submit questions,” Johnson said. “I already have. Awaiting a response. Not holding my breath.”

Some lawmakers are now calling for the resignation of Secret Service Director Kimberly Cheatle.

“Last week’s near-assassination of former President Trump was a grave attack on American democracy,” Senate Minority Leader Mitch McConnell, R-Ky., said in a statement posted on X. “The nation deserves answers and accountability. New leadership at the Secret Service would be an important step in that direction.”

On Wednesday, Republican Rep. James Comer, chair of the House Oversight and Accountability Committee, issued a subpoena to secure  Cheatle’s appearance at a hearing set for Monday, according to The Hill.