Among the claims made in a new book about former US President Richard Nixon is the suggestion that he may have had a gay relationship with one of his closest confidants.

The author of the book, Nixon’s Darkest Secrets: The Inside Story of America’s Most Troubled President, suggests Nixon’s relationship with Charles “Bebe” Rebozo, a banker with Mafia connections, could have been more than platonic.

Don Fulsom, a longtime White House reporter and former Washington bureau chief for the United Press International agency, teaches a module on Nixon’s Watergate scandal at the American University in Washington, DC.

His book alleges that by the time Nixon became president in 1969, he had been linked to the mob for more than two decades and maintained a close connection with New Orleans mob boss Carlos Marcello, the most powerful Mafioso in the US.

And, after interviews with those who were connected with him at the US Congress, in the White House and in other ways, Fulsom claims Nixon, who died in 1994 the only US president ever to have resigned, may have had a gay relationship with Rebozo.

Rebozo reportedly had an office and a bedroom at the White House and high-level security clearance before Nixon’s resignation in 1974.

He had had a four-year marriage which was never consummated, and a subsequent marriage in which his wife complained she came third in his affections behind the President and Rebozo’s cat.

It has never been made clear why Rebozo’s Mafia connections, documented by the FBI, did not stop him fraternising with Nixon when he became President.

Nixon was not himself averse to using claims of homosexuality to smear opponents. He intended to tarnish his opponents’ reputations by associating them with the nascent gay rights movement.

During the 1972 election campaign, Nixon aides also tried to link Democrat candidate John McGovern and his running mate Sargent Shriver to the mafia, slavery and left-wing activists.

In 1964, Walter Jenkins, an aide of Lyndon B Johnson was forced to resign. He had worked closely with Johnson since 1939, but when he was arrested by police in Washington DC performing oral sex on a man in a YMCA bathroom he was forced to stop down.

At the time, Nixon described him as “ill” and said he should not have held a position of “high trust”.

Nixon biographer Anthony Summers told the Daily Mail there was no evidence to suggest Nixon had a sexual relationship with Rebozo.

He said: “They held hands on occasion, and both men had problems with consummating physical relationships with women, but we found no evidence that Nixon was actively homosexual.”

The new book also includes a testimony that the former president had ordered the killing of White House reporter Jack Anderson.