It has been the Secret Service’s protocol for more than a half-century since the assassination of John F. Kennedy — survey and secure all nearby structures to prevent gunfire from reaching a president or anyone else under the agency’s protection.

But somehow on Saturday, a 20-year-old Pennsylvania man was able to access a roof with a gun just 140 yards from the stage where former president Donald Trump was speaking.

Now the Secret Service’s actions and the potential holes in its protective net are under intense scrutiny, with lawmakers in both parties calling on Secret Service Director Kimberly Cheatle to account for her decisions and law enforcement officials and experts expressing shock at what many said was the worst Secret Service breakdown since the assassination attempt on President Reagan in 1981.

“There are many questions and Americans demand answers,” Rep. James Comer (R-Ky.), chairman of the House Oversight Committee, wrote to Cheatle in a letter asking her to testify later this month.

Joe Hagin, who as a senior White House official in the Trump and George W. Bush administrations worked closely with the Secret Service, called for a top-to-bottom review of how this could happen.

“For the good of all the protectees from the president on down, we need to have a thorough and fair investigation by people who know what they’re talking about,” Hagin said.

The shooting, in which Trump was injured and guided offstage by agents while blood dripped down his face, raises new questions about an agency that is both revered for its role in safeguarding the lives of American presidents but has for years endured intense pressure amid staffing shortages and repeated security lapses.

Kevin P. Rojek, the FBI special agent in charge of the Pittsburgh field office, said it was “surprising” that the gunman was able to open fire on the stage before being killed.

Responding to questions from The Washington Post, Secret Service spokesman Anthony Guglielmi confirmed Sunday that the agency relied on local police at the Trump rally to fill out significant parts of its typical array of specialized protective units — including its heavily armed counter assault team that provided cover as Trump’s detail evacuated him and the counter sniper teams that ultimately spotted and killed the shooter.

The Service had two of its counter assault agents on the scene and filled out the rest of the typical platoon with at least six members of Butler County tactical units, Guglielmi said. Two Secret Service counter sniper teams were on the scene, but two additional teams that had been recommended for adequate protection at the rally were staffed by local units, he said.

When asked about the role of local police in securing the event, George Bivens, a lieutenant colonel with the Pennsylvania State Police, told reporters local officials typically provide support for such VIP visits, but takes its instruction from the Secret Service.

“Secret Service always has the lead on securing something like this,” Bivens said. “We work with them to provide whatever is requested by the Secret Service, but they’re the lead in that security.”

Rep. Ritchie Torres (D-N.Y.) and Michael Lawler (R-N.Y.) announced Sunday they are introducing a bill that would give enhanced protection to the three candidates: Trump, President Biden and Robert F. Kennedy Jr. “Last night’s attempted assassination of former President Trump was a dark moment in our nation’s history. As reports continue to emerge, it’s clear that more protection is needed for all major candidates for president. That’s why we’re planning on introducing bipartisan legislation providing President Joe Biden, former President Donald Trump, and presidential candidate Robert Kennedy Jr. with enhanced Secret Service protection. Anything less would be a disservice to our democracy,” the representatives said in a joint statement.

The shooting highlighted tensions over how the agency has been planning to safeguard major campaign-related events as the election nears — including the Republican National Convention scheduled to take place this week in Milwaukee.

A senior Republican involved in Trump’s election effort said there had been months of disagreements with the Secret Service over the convention, with Trump’s team believing the Secret Service did not take the threats of violent protests and demonstrations seriously enough. Several of the calls had grown acrimonious. This person said that both sides had grown to distrust one another — and “there will be a demand for answers on how a gunman could get on a roof that close to Trump and have a clear shot at him.”

The Secret Service pushed back Sunday on claims made by some Republicans after the shooting that Trump or his security detail asked for more security and was denied it. A spokesman for the agency said that extra agents were added to the security details of Trump, Biden and Vice President Harris as the frequency of their campaigns increased in the last two months or so.

“The assertion that a member of the former President’s security team requested additional security resources that the U.S. Secret Service or the Department of Homeland Security rebuffed is absolutely false,” Guglielmi said. “In fact, recently the U.S. Secret Service added protective resources and capabilities to the former President’s security detail.”

Guglielmi continued: “The former President, and the current President, are commonly subject to threats. The U.S. Secret Service takes threats seriously, and it takes actions based on those threats as warranted. The U.S. Secret Service is constantly evaluating the very dynamic threat environment and responding to it in the fulfillment of its responsibilities.”

Secret Service agents, both current and retired, told The Post that they are in shock at how badly Trump’s outer rings of security appeared to fail. They note that the inner perimeter of Trump’s security, the agents in his immediate detail, performed rapidly once shots rang out and evacuated Trump to safety upon confirming the shooter had been killed and was no longer a threat.

“How the f--- did he get a gun that close,” one former Secret Service officer opined in a series of exchanges with colleagues yesterday reviewed by The Post. The response he received from a fellow agent was “resources.”

Some watching videos of the shooting pointed to the outer ring of security as the gaping flaw. A well-respected counter sniper agent ultimately killed the suspected shooter within seconds of him firing.

“This is bad. Just terrible,” said one former senior leader of Secret Service presidential protection, speaking on the condition of anonymity to discuss the agency. “When the incident occurred I was baffled when I heard the distance of the shot ... How could that happen?”

Jason Chaffetz, a former chair of the House Oversight Committee who produced a sweeping 2015 investigative report on Secret Service security failures and the agency’s being stretched too thin, said he is deeply disturbed that the same problems identified nearly a decade ago remain and appear to have contributed to failure to detect the shooter at the Saturday rally.

“This was a catastrophic failure. It should never have been a remote possibility,” Chaffetz said in an interview. “We did all these investigations and did an extensive report so this would never happen again. It’s as if they paid no attention to the bipartisan recommendations.”

Speaking Sunday on CNN’s “State of the Union,” Andrew McCabe, former deputy director of the FBI, said that “one of the most basic elements” of securing a site is to eliminate sight lines to the place where a protected person will be speaking. Looking at Saturday’s shooting, he said that buildings just outside of the traditional perimeter of an event should have been noted as within shooting range. Law enforcement typically either puts people around or on top of such buildings or places obstacles between them and where a protected person is standing, he added. “So I think preliminarily there are going to be a lot of questions about why those steps weren’t taken here,” McCabe said. He noted that it’s important not to jump to conclusions but said there are “many questions to be answered in light of what we now know.”

Aaron Shaffer and Brittany Shammas contributed to this report.

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