A local cop spotted attempted-assassin Thomas Crooks just moments before he tried to kill former president Donald Trump — but failed to stop the gunman despite the clear threat, according to a report.

After rallygoers spotted Crooks on the roof of a manufacturing plant just 130 yards from the stage where Trump was speaking just after 6 p.m. Tuesday, police were notified and one officer climbed a ladder to investigate, law enforcement officials told The Associated Press on the condition of anonymity.

The officer – whose department had been enlisted by the Secret Service to help with security — encountered Crooks, who pointed his AR-style rifle at them.

The officer then backed down the ladder, and Crooks immediately took aim and loosed about eight shots at the former president – grazing him in the ear, killing one bystander in the rally crowd, and gravely wounding two others, the source said.

Despite the Secret Service’s quick response taking out the shooter, the agency tasked with protecting former and current presidents’ lives is facing harsh scrutiny for allowing a gunman to establish an open position so close to Trump’s rally.

“This was a catastrophic failure. It should never have been a remote possibility,” former House Oversight Committee chair Jason Chaffet, who lead an extensive 2015 investigation into the shortcomings of the Secret Service in 2015, told the Washington Post.

“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,” said Chaffet, whose report focused on ways the Secret Service had been spread too thin.

The Secret Service confirmed after the shooting that it relied heavily on local police to help support its security efforts at the rally, including at least six officers from Butler County tactical units supporting the counter assault team that covered Trump’s evacuation – which only included two officers from the Secret Service, according to the Washington Post.

There were also two Secret Service sniper teams on sight, and an additional two were staffed with local officers.

“Secret Service always has the lead on securing something like this,” Pennsylvania State Police lieutenant colonel George Bivens told reporters, explaining that local police are routinely enlisted to help the Secret Service.