US Secret Service Director Kimberly Cheatle resigned yesterday, a day after acknowledging that the agency failed in its mission to prevent an assassination attempt against Donald Trump.

Cheatle was facing bipartisan calls to step down after a 20-year-old gunman wounded the former Republican president and current White House candidate at a July 13 campaign rally in Butler, Pennsylvania.

"It is overdue, she should have done this at least a week ago," Mike Johnson, Republican Speaker of House of Representatives, said.