An independent panel investigating the attempted assassination of former US president Donald Trump at a Pennsylvania campaign rally says the Secret Services "needs fundamental reform" and that "another Butler can and will happen again" without major changes in how candidates are protected.
The review faulted the Secret Service for poor communications that day and failing to secure the building where the gunman took his shots.
It also found more systemic issues at the agency such as a failure to understand the unique risks facing Trump and a culture of doing "more with less".
The 52-page report issued on Thursday recommended bringing in new, outside leadership and refocusing on the Secret Service's protective mission.
"The Secret Service as an agency requires fundamental reform to carry out its mission," the authors wrote to Secretary Alejandro Mayorkas of the Homeland Security Department, the Secret Service's parent agency, in a letter accompanying their report.
"Without that reform, the Independent Review Panel believes another Butler can and will happen again".
One rally-goer was killed and two others wounded when Thomas Matthew Crooks climbed onto the roof of a nearby building and opened fire as Trump spoke.
The former president was wounded in the ear before being rushed off the stage by Secret Service agents.
That shooting, along with another incident in Florida when Trump was golfing - a gunman there never got a line of site on Trump or fired a shot - has led to a crisis in confidence in the agency.
The report by a panel of four former law enforcement officials from the federal and state government follows investigations by members of Congress, the agency's own investigators and by Homeland Security's oversight body.
The Secret Service said it was making changes.
"We have already significantly improved our readiness, operational and organisational communications and implemented enhanced protective operations for the former president and other protectees," the agency's acting director Ronald Rowe said in a statement on Thursday.
The agency said it was looking at how to retain personnel, modernise technology and bolster training, and was working with Congress to increase funding.
The panel echoed previous reports that have zeroed in on the failure to secure the building near the rally that had a clear line of site to where Trump was speaking and the multiple communications problems that hindered the ability of the Secret Service and local and state law enforcement to talk to each other.
The panel faulted the planning between Secret Service and the local law enforcement, and said the Secret Service failed to ask about what was being done to secure the building: "Relying on a general understanding that 'the locals have that area covered' is simply not good enough and, in fact, at Butler this attitude contributed to the security failure".
The review questioned why there were two separate command posts at the rally and found other communications problems, including the need to switch radio channels because radio traffic from agents protecting first lady Jill Biden at an event in Pittsburgh was coming across the channels of agents who were with Trump.
Also, law enforcement personnel on the ground used a "chaotic mixture" of radio, mobile phone, text and email.
And it was unclear who had ultimate command that day.
The panel recommended new leadership, specifically from outside the agency, but the report did not say whether anyone should be fired.
Other recommendations included: having a unified command post at all large events; overhead surveillance for all outdoor events; security plans that specify how to mitigate line of site concerns out to 1000 yards and who is in charge; and more training on how to get protectees out of dangerous scenarios.
But this is not the first time that an independent review has found fault with the agency.
After a man jumped the White House fence and evaded Secret Service to run into the building, a panel a decade ago looked into how the agency protects the White House.
It recommended some of the same changes.
