Reagan switched to the Republican Party in 1962. As noted elsewhere, he was never a liberal, but saw as early as 1962 that the Democratic Party was becoming more and more liberal. It was in 1962 that he proclaimed, “I didn’t leave the Democratic Party. The party left me.”
I guess the real point is that Reagan never espoused contemporary liberal ideals and that he had been a Republican for almost 18 years when he ran for president.
that’s not a small difference.