US Secret Service 'failed' in mission to protect Trump: director

"The Secret Service's solemn mission is to protect our nation's leaders," Cheatle said during testimony before the House Committee on Oversight and Accountability.

"On July 13, we failed," she said. "As director of the United States Secret Service, I take full responsibility for any security lapse."

Cheatle, who is facing bipartisan calls to resign, said the assassination attempt on Trump, who was slightly wounded in the ear while speaking at a campaign rally, was "the most significant operational failure of the Secret Service in decades."

The 20-year-old gunman, Thomas Matthew Crooks, opened fire on Trump with an AR-style rifle just minutes after the former Republican president and current White House candidate began speaking at a campaign event in Butler, Pennsylvania.

Crooks was shot dead by a Secret Service sniper 26 seconds after firing the first of eight shots.

Investigators have determined that Crooks, who lived in a town about 50 miles (80 kilometers) from Butler, acted alone and have not been able to identify any strong ideological or political leanings.

Two rally attendees were seriously wounded in the shooting and a 50-year-old firefighter, Corey Comperatore, of Freeport, Pennsylvania, was shot dead.

Opening the hearing into the assassination bid, Republican committee chairman James Comer said "this tragedy was preventable" and "it is my firm belief, Director Cheadle, that you should resign."

"The Secret Service's protective mission is to protect US and visiting world leaders and safeguard US elections through protection of candidates and nominees," Comer said.

"The Secret Service has a zero-fail mission, but it failed on July 13 and in the days leading up to the rally," he said.

"The Secret Service has thousands of employees and a significant budget, but it has now become the face of incompetence."