It’s well-known, of course, that Ronald Reagan was once a Democrat, but when exactly did he cast his first ballot for a Republican? When I was researching my book Tricky Dick and the Pink Lady, all signs seemed to point to the infamous 1950 race for the US Senate in California between Richard Nixon and Helen Gahagan Douglas.

Reagan, in the mid-1940s, had flirted with leftish groups and even ended up on one of Myron Fagan’s blacklists. He was considered so far left that Douglas organizers would not let him take a public part in her maiden race for Congress that in 1944, deemng him “too hot to handle,” as one of them put it. (The writer Howard Fast later claimed, rightly or not, that Reagan “desperately” wanted to join the Communist Party.) But a few years later he apparently agreed to serve as an FBI informant on Screen Actors Guild (which he headed) activities, with the ID number of “T-10,” and appeared as a friendly witness before the House Unamerican Activities Committee.

Obsessed with politics, Reagan had drawn interest as a candidate himself for the Senate seat in 1950 but did not jump at it. Instead he continued his anti-Communist drive, and wrote a guest column for Victor Reisel in which he declared, “We’ve gotten rid of the Communist conspirators in Hollywood,” and called on all exposed Reds to rat on their former associates.

At some point early in 1950, Reagan donated $50 to the Douglas campaign but when her managers went back for more they were rebuffed. On October 23, Douglas sent him a brief note thanking him for his “help and support,” but it was quite cool, addressing him not as Ron or Ronnie but “Ronald Reagan.”

By then his support for Douglas had evaporated. For almost a year he had been dating the politically conservative actress Nancy Davis. One of Nancy’s best friends was Zasu Pitts, a pal of J. Edgar Hoover and a leading Nixon activist in Hollywood. Earlier that year, Zasu had phoned Hedda Hopper to report that in the mid-1930s, Helen and husband Melvyn Douglas had helped organize a farmers’ union in South Carolina that was later revealed to be a Communist front. Later she smeared Helen Douglas so savagely the candidate considered suing her for slander. Nancy Davis at one point took Reagan to a meeting where Pitts railed against Douglas.

Reagan was close to another Nixon activist, actor Dick Powell. In previous years, they argued heatedly about politics, but then came 1950. Powell’s wife, actress June Allyson, later explained, “I do not whether it was Richard [Dick Powell] or Nancy and her staunchly Republican family who finally switched Ronnie. I only know that Richard, chortling with glee, took full credit for it.”

One night, not long before election day, actor Robert Cummings received a phone call from Reagan (he wrote in a memoir). Cummings had Republican leanings but not strong ones, and had his own political disputes with Reagan when they acted in King’s Row in 1942. Cummings considered Reagan one of the most honorable men in town and joked that he ought to run for president some day.

Cummings would re-create that phone conversation this way:

“I’m trying to help a senator get elected and we’re giving a party for him tomorrow night,” Reagan reportedly said. “Can you come?”

“Who is the senator?”

“His name is Richard Nixon.”

“But isn’t he a Republican?”

“I’ve switched,” Reagan announced, according to this account. “I sat down and made a list of the people I know, and the most admired people I know are Republicans.”

Of course, Cummings may have imagined this; no evidence of Reagan hosting a party has turned up. But his lack of offering further help, or money or any support for Douglas in the fall campaign — despite efforts to secure any of it — supports the view that indeed he did back Nixon on election day.

Greg Mitchell’s latest book is The Age of WikiLeaks: From Collateral Murder to Cablegate (and Beyond).