To put it simply the Republican Party has moved away from Ronald Reagan. When President Reagan was in office in the 1980s he was that unifying force that could keep a large and very politically diverse political party together because they all lived Reagan.
The real Conservatives the Barry Goldwater faction that still makes up the conservative libertarian wing of the party. The emerging Religious-Right, or as I call them the big government wing of the party. And the business Conservatives who are really not interested in social issues and only foreign policy as it relates to the economy. And of course the Neoconservatives defense hawks that were inline with the Religious-Right on social issues. But perhaps further to the right of them on foreign policy. President Reagan was able to keep all the different GOP factions together and not going off in directions and focused at beating Democrats.
That type of leader that Reagan was for the GOP have never been replaced. And they haven’t that one person that can keep the party together. So you are left with a Republican Party with all of these different tribes accusing each other of not being real Republicans and on many cases mad at each other. But the other issue that would be there for Reagan is that as much as Republicans like to call themselves Reagan Republicans, they really aren’t. He wasn’t inline with them on the social issues in many cases. He just spoke to those groups because he wanted their support. And he wasn’t as big a unilateralist defense hawk for today’s Neocons.
The closest Republicans to Ronald Reagan and his vision of conservatism or conservative libertarianism would be the Rand Paul conservative libertarian wing of the party. People who are viewed by the Religious-Right and Neoconservatives as not real Republicans and far enough to the right for them. And because of these things Ron Reagan would have a hell of a time running for president as a Republican today.