It all comes down to some basic mathematics. Now, before the modern Internet, every village, town, and city had a FEW people who were considered a village idiot, conspiracy theory nut, or "crazy". The local people knew who they were, and knew to ignore what those people would say. Then, the Internet showed up, and everyone got access. A strange thing happened, suddenly we saw just how many of those "village idiots" there were, all those small towns, or cities, the crazies started organizing. When the overall numbers get counted, they might amount to 10% or less, but when elections are often within 5%, that 10% would mean the difference between winning an election or losing it.
So, the Republicans decided to embrace that segment of the populace, and gave them more power than at any time in history, to the point you see people like Marjorie Taylor Greene actually winning elections and getting into office, and then getting reelected. Then, the rest of the Republican Party embraced them and let them get leadership positions. In the same way that conservatives have had control over the DNC(you see it when Joe Manchin was looked on so favorably while ANY progressive would have the DNC try to primary them out of office), the crazies have taken over the Republican Party.
And all of this is because both parties keep nominating bad candidates for elections, so you get an even split of people who are disgusted by both choices, so just vote on party lines. If people win by only 5%, that's showing a person who isn't accepted by a true majority of people.