I would say instead that the definition of conservatism has changed. I consider myself an “Eisenhower Republican”…and the 1956 GOP party platform under Eisenhower had much in common with the 2012 Democratic party platform under Obama.
I happily voted for Reagan and Bush 41…but I saw where the GOP was going in the early 1990’s, and I became a Democrat and am now a strong liberal. Reagan once said that he didn’t leave the Democratic Party, but it left him instead. With me, it’s the converse: I didn’t leave the GOP, but the GOP left me.
It’s been often noted that Reagan and Bush 41 would both stand no chance in today’s GOP. I’d go further and say that neither Ike nor even Goldwater would stand a chance…because today’s conservatives aren’t conservative at all, but reactionary populists, effectively a mob led by a demagogue who tossed every real conservative value over the side for the sake of power and racism.