‘It was unacceptable’: Secret Service head breaks silence after Trump shooting as questions swirl over how it unfolded

The head of the Secret Service has admitted that it was "unacceptable" for an armed assassin to come so close to killing former president Donald Trump.

In her first public comments since Saturday's shooting, agency director Kimberly Cheatle said the gunman should never have been allowed to get in a position to take his shot and that "the buck stops with [her]".

"It was unacceptable, and it's something that shouldn't happen again," Cheatle said in an interview with ABC News on Monday.

"It was obviously a situation that as a Secret Service agent, no one ever wants to occur in their career. The buck stops with me... and I need to make sure that we are performing a review and that we are giving resources to our personnel as necessary."

However, Cheatle said she would not resign from the role despite questions about the Secret Service’s preparation and handling of the rally. She is expected to testify before a House of Republicans committee on July 22.

She also repeated that the assassin's perch was outside the area that had been secured by her agents, with responsibility instead falling to the local police department.

Questions, criticisms, and conspiracy theories have swirled around the Secret Service ever since 20-year-old Thomas Matthew Crooks crawled up onto a roof less than 150 meters away from Trump's podium and opened fire with a semi-automatic rifle.

Witnesses claim that they tried to warn law enforcement agents about a suspicious man on the roof several minutes beforehand, and police did see signs of trouble. The USSS also had counter-sniper teams on the scene whose task was to watch for and respond to long-range threats.

Officials have said that a local police officer tried to climb onto the roof and investigate, but was forced to let go and drop painfully to the ground when Crooks swung his weapon towards him. Crooks then apparently wheeled, aimed and fired at Trump, before being shot dead himself by a sniper.

"This was a security breakdown from start to finish," former FBI assistant director Chris Swecker told Fox News on Sunday. "The primary mission of the Secret Service is to prevent this type of action."

Former Secret Service agent Jonathan Wackrow told The Independent that "a lot of questions remain unanswered", saying the service must immediately review what happened and whether its procedures need to be changed before candidates in this year's election are exposed to further violence.

In her ABC interview, Cheatle said local police had been tasked with securing the building from which shots were fired, and that they had officers inside it while the shooter was scaling the roof.

She fully backed the sniper's "split-second decision" to shoot back, saying: "They have the ability to make that decision on their own. If they see that it's a threat and they did that in that instance.

"And I applaud the fact that they made that decision and didn't have to check with anybody, and thankfully neutralized the threat."

She also rejected any accusation of political bias within the Secret Service, saying: “Secret Service is not political. Security is not political. People's safety is not political. And that's what we're focused on as an agency.”