Richard Nixon was many things — crafty, criminal, self-pitying, vengeful, paranoid. But gay?

According to a book to be released Tuesday, “Nixon’s Darkest Secrets,” the former president and his best friend, Charles “Bebe” Rebozo, had a relationship of a “possibly homosexual nature.” But author Don Fulsom, a former radio reporter who covered the White House from Lyndon Johnson’s presidency to Bill Clinton’s, provides scant evidence for this claim. No new White House tapes. No love letters, incriminating pictures or diary entries. No recently declassified government documents. Just a recollection from retired journalist Bonnie Angelo, who, in an interview with me, confirmed the story she told Fulsom: In 1972, she saw a tipsy Nixon pull Rebozo into a group photo at a Florida restaurant and hold his hand for “upwards of a minute.”

That’s pretty thin gruel — but not so thin that it keeps the author from enthusiastic speculation. “Was Nixon’s tough-guy attitude toward gays just a cover for his own homosexuality, bisexuality or asexuality?” Fulsom writes. “Well, he isn’t still called ‘Tricky Dick’ for nothing.”...