Guy - no offense meant, but I think you are reading a revisionist history of the Reagan years or did not know or have forgotten (I don't know your age) the threat to democracy we had worldwide under the Soviet threat. Reagan wasn't perfect and in an era of peace it is easy to pick any administration apart - esp 40 years removed from that history.
The division we are seeing now was totally not imaginable during the time of Reagan - who didn't mind having a drink with the Democratic House leader. There are many reasons top historians have placed Reagan in the top 10 realm of presidents and linking him to the trumpian, Neanderthal, fascist world of today's GOP is not one of those reasons.
But I think we can go to the scorched earth campaign of GHWB run by Lee Atwater and we start seeing a bit more of what you are talking about. Jump that up a notch with
Newt. After the GOP got a taste of power, owning the House after 38 years, then we start seeing more issues that led to deeper divisions. But even at that, the Tea Party and then Trump himself took it to a whole new level.