[jhp123]

I mean everything has been around but we're talking about mainstream acceptance. Trump said that the elections were stolen and the violent riots were justified. What major figure from either party supported anti-government violence before?

Voting fraud was a talking point going back at least to Von Spakovsky under Bush but this was a minor figure who wasn't taken very seriously at the time. Now it's supported by the party leadership.

The moderate Republican party elites were in control up to the tea party movement. This was what the tea party itself was saying: our views are not being represented. Mottos like "America First" and "Drain the Swamp" were relegated to third-party candidacies like Buchanan 2000.

BTW there has been movement on the left too, I'm focusing on the right because that's what you asked about. The 1990s were a moment of remarkable elite consensus with the centrist DLC in control on the left and the more moderate GOP factions on the right. This led to memes about "both parties are the same" like "Kang and Kodos" (1990) and "Giant Douche vs Shit Sandwich" (2004). Since then American politics have polarized and the parties have moved much further apart. The concept of an "Overton window" doesn't even make as much sense anymore, because many people take offense at mainstream views of the other side (e.g. "trans women are women" or "Jan 6 was justified because the 2020 election was stolen by Biden")