An investigation was underway by the US Secret Service after a man who seemed drunk and disoriented bypassed agents and entered the Washington home of Joe Biden’s national security adviser.

The Washington Post reported that Jake Sullivan told a man who had entered his Washington home to leave. The incident happened around 3am one night in late April and there was no forced entry.

The Post said: “Sullivan has a Secret Service detail 24/7. But agents outside the house did not know an intruder was inside … until the man left and Sullivan came out to tell the agents.” A Secret Service spokesperson said: “We are taking this matter seriously and investigating what occurred. Any deviation from our protective protocols is unacceptable and personnel will be held accountable if discovered.

We have also made modifications to the protective posture to ensure more security layers as we conduct this review.” National security advisers got more protection after an alleged Iranian plot to kill John Bolton, Donald Trump’s third such adviser, was discovered in 2021. Carol Leonnig, a Post reporter and author of a recent book on the Secret Service, told MSNBC that the Bolton plot was “a reason sources reached out to us”.

She said: “An Iranian military official has been charged with paying someone to try to kill [John Bolton] on US soil. That’s why Jake Sullivan has 24/7 protection, and we would hope as Americans that protecting him would be tighter than someone getting into his home in the middle of the night.”

Attacks on US politicians and public officials are a growing concern. Last October, a man with a hammer attacked Nancy Pelosi’s husband, Paul Pelosi, at their San Francisco home. Nancy Pelosi is the former US House speaker and is guarded by US Capitol police.

Earlier this week, a man with a metal baseball bat attacked staff and damaged property at the district office of Gerry Connolly; Connolly, a Democratic member of Congress, was not there. Two staffers went to hospital. The man, 49, had a history of mental illness, reports said.

The Post said the intruder at Sullivan’s house did not mean to harm him. But Secret Service lapses are always high-profile because they protect senior officials.

In 2009, a state dinner for the prime minister of India, which was Barack Obama’s first as president, was crashed by a socialite couple who sought reality TV fame.

A man who scaled a 5ft fence by the US treasury department and spent 16 minutes on White House grounds caused a more alarming incident in 2017. He carried two cans of Mace spray, a passport, a computer and a book by Donald Trump.

He told agents he was the president’s friend and had an appointment. Trump was home at that time. Leonnig said of the incident at Sullivan’s home: “The real big alarm bell here is that the Secret Service was unaware that a person entered his house in the middle of the night.” Warrick, an Atlantic Council member and security expert, told CBS News: “This should not have happened. Absolutely not. And especially where hostile nation states target US officials on US soil.”