US Secret Service Director Kimberly Cheatle has resigned after the agency came under harsh scrutiny for its failure to prevent an assassination attempt on Donald Trump.

The Secret Service, which is responsible for protecting current and former US presidents, faces a crisis after a gunman was able to fire on Trump from a roof overlooking the campaign rally in Butler, Pennsylvania on July 13.

“The independent review to get to the bottom of what happened on July 13 continues, and I look forward to assessing its conclusions,” Democratic President Joe Biden said.

“We all know what happened that day can never happen again.”

Homeland Security Secretary Alejandro Mayorkas said deputy director Ronald Rowe, a 24-year Secret Service veteran, would be acting director.

The Secret Service faces investigations from multiple congressional committees and the internal watchdog of the US Department of Homeland Security, its parent organisation, over its performance.

Biden, who has ended his re-election campaign, has also called for an independent review.

“I take full responsibility for the security lapse,” Cheatle said in an email to staff on Tuesday, the Associated Press reported.

“In light of recent events, it is with a heavy heart that I have made the difficult decision to step down as your director.”

Cheatle faced bipartisan condemnation when she appeared before the House of Representatives Oversight Committee on Monday (US time), declining to answer questions from frustrated lawmakers about the security plan for the rally and how law enforcement responded to the suspicious behaviour of the gunman.

Several Republican and Democratic lawmakers called on her to resign.

Trump, the Republican presidential candidate, was grazed in the right ear and one rally attendee was killed in the gunfire.

The gunman, identified as a 20-year-old Thomas Crooks, was shot and killed by a Secret Service sniper.

“While director Cheatle’s resignation is a step toward accountability, we need a full review of how these security failures happened so that we can prevent them going forward,” James Comer, the Republican chair of the House Oversight Committee, said.

“We will continue our oversight of the Secret Service.”

Cheatle, who has led the agency since 2022, told lawmakers she took responsibility for the shooting and called it the agency’s largest failure since then-president Ronald Reagan was shot in 1981.

House leaders said on Tuesday they planned to form a bipartisan task force to probe the shooting.

Much of the criticism has focused on the failure to secure the roof of an industrial building where the gunman was perched about 140 metres from the stage where Trump was speaking.

The rooftop was declared outside the Secret Service security perimeter for the event, a decision criticised by former agents and politicians.

Cheatle held a top security role at PepsiCo when Biden named her Secret Service director in 2022. She previously served 27 years in the agency.

She took over following a series of scandals that scarred the reputation of an elite and insular agency.

Ten Secret Service agents lost their jobs after revelations they brought women, some of them prostitutes, back to their hotel rooms ahead of a trip to Colombia by then-president Barack Obama in 2012.

The agency also faced allegations that it erased text messages from about the time of the January 6, 2021, riots on the US Capitol.

Those messages were later sought by a congressional panel probing the riot.

-with AP