NEW YORK - A US Senate report on the assassination attempt targeting US President Donald Trump last year has revealed "multiple, unacceptable failures" in the Secret Service's discipline.

The report came a year after Trump, then a presidential candidate, was grazed by a bullet as a 20-year-old gunman fired eight shots at him at a campaign rally in Butler, Pennsylvania.

The gunman was killed by a sniper subsequently. But the shooting, killing one attendee and injuring two, exposed the Secret Service's negligence in planning and response, said the report, calling for more severe disciplinary action.

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"What happened was inexcusable, and the consequences imposed for the failures so far do not reflect the severity of the situation," said the report by the Senate's Homeland Security and Governmental Affairs Committee.

"This was not a single lapse in judgment. It was a complete breakdown of security at every level -- fueled by bureaucratic indifference, a lack of clear protocols and a shocking refusal to act on direct threats," said Rand Paul, the committee's Republican chairman, in a statement.

Mentioning that Secret Service became aware of a suspicious individual "nearly 45 minutes before shots were fired, and failed to act," the report noted a series of errors that expose "a disturbing pattern of communication failure and negligence that culminated in a preventable tragedy."

"We must hold individuals accountable and ensure reforms are fully implemented, so this never happens again," Paul said.

The director of the Secret Service, Kimberly Cheatle, resigned after the shooting, and six other agents on duty received suspensions from 10 to 42 days, the agency said on Thursday.

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But no one was fired, and the penalties were lighter than the committee had recommended.