There is a very interesting read, which is a review of two books, one a biography and the other an autobiography. The article appeared in New Republic sometime in the late 80s or early 90s. It can be found here.
The story is long and complicated. Excerpt: "Whatever his reasons for turning against communism, he remained left of center long after he did so. As late as 1952, by which date he had been publicly denouncing Communists for six years, the Los Angeles County Democratic Central Committee declined to endorse him for an open House seat because they thought he was too liberal. It's tantalizing to speculate on what might have been had the Democrats of Los Angeles not made this bonehead decision. Would Representative Reagan have become Senator Reagan? Might he have ended up as JFK's running mate? Would he have drifted to the right and become a marginal crank like Sam Yorty? Or would he have stayed left and won the White House four or eight years earlier than he did? And — most delicious thought of all — would the ultimate sneer-word of today's conservatives be not McGovernism or Carterism, but Reaganism?"