The mainstreaming of right wing lunacy started started to form during the Republican revolution Newt Gingrich years when they started taking this confrontational obstruction stance, and suggesting Clinton is somehow not legitimate or “not my president.” Of course it seems mild compared to what they did in the Obama years but it was still unprecedented in modern American history. And Clinton was a white guy from Arkansas, but just being a 60’s liberal hippie (who later sold out) was enough for the hard right to see his neoliberal ass as some kind existential threat.
The rise of talk radio around that time contributed a lot to the radicalization. Of course you have Timothy McVeigh, abortion clinic bombers, and a record rise in militia membership, but it was still fringe.
From there, you get this disturbing jingoism/nationalism manifesting itself in the support of Middle east warmongering during the Bush years, and the further demonization of all “liberals” as un-American.
Then you had the mini-rise of that dolt Sarah Palin (thanks John McCain), and the tea party, the precursors to Trump and MAGA. They're only going to get crazier.