It's all interesting and well-researched.

Caveat: I'm British.

A few areas of disagreement.

I don't think that the 80s were a time of bipartisan consensus in America. It was on foreign policy (since the WW2). The Reagan revolution massively upended things and brought in the neoliberal era. On economics, the Democrats were divided into those who wanted to fight Reaganism and those who wanted to go along with it, with the latter winning out by the Clinton era.

The 90s were the time of least polarisation due to what I just mentioned and the end of the USSR as an existing alternative model. The time of greatest polarisation is now.

However, the polarisation is asymmetrical. The Democrats haven't moved that much in recent years. They have a radical social democratic wing but it's marginalised and they tied to the same consensus (economic and foreign policy) that both parties used to follow. They have become more liberal on social issues and Biden was a tepid step to the left but it certainly wasn't a radical change.

It's the Republicans who have radicalised and are upending the existing order.

For various reasons (some of which you mention) the far-right takeover is more advanced in America than in any other major country but you will know as well as I do that the nationalist right is rising across Europe and elsewhere.

Why?

There are lots of factors. The relative geopolitical decline of the West, internet conspiracy theories and the decline in organised labour. The slow collapse of trust in mainstream institutions and a revival in nationalist identities.

There is also the point that the neoliberal era once brought about rapid growth and increases in living standards but is no longer able to do so. Though there is still spirally wealth inequality which produces resentment. As someone who I suspect is a classical liberal, you might disagree on that point.

A few points.

Reagan was elected with Republicans taking over control of the U.S. Senate (and held it for six of his eights years). And there was still a good enough number of conservative Democrats in the House that went along with parts of Reagan's economic policies.

Bush 41, however, had to deal with Democrat majories in both the Senate and the House. And the economic downturn in 1992, and the challenge from Pat Buchanan, evaporated his 91% approval rating at the end of the Gulf War.

Then enter H. Ross Perot.

Others will disagree, but I am convinced that had Perot not entered the presidential race, Bush would have won re-election. Yes, I know of the exit poll questions supposedly being split on the Bush or Clinton choice among Perot voters. ( see, for example: https://split-ticket.org/2023/04/01/examining-ross-perots-impact-on-the-1992-presidential-election/ )

But what those exit polls don't tell you is that with Perot forcused almost all his energy on attacking Bush; all the negative attention was on President Bush. Had Perot not ran, Clinton would have faced far more scruntiny. Many of those Perot voters were influenced by all the attacks on Bush. Would a slim majority of them still have favored Clinton had Perot not ran? I do not believe so.

As to when the radicalization of American politics, when the growing divergence began to occur, I would point to 1994.

That's when the Republicans gained control of the House for the first time since Eisenhower's presidency. The grabbed the Senate, too, and defeated two of the most popular Democrat governors in two of the nation's biggest states: New York's Mario Cuomo and Texas' Anne Richards. Speaker Tom Foley (D-WA) lost his re-election bid for his House seat. And Newt Gingrich would be the new Speaker of the House.

Furthermore, as we've seen since 2016, it was a different type of Republican that was being elected. Radical is certaintly the word. But the Democrats share much of the blame for their own losses. They didn't take the possibility if losing the House seriously. The failed to realized that Clinton's victory in 1992 was not a mandate. And Clinton himself failed to take advantage of passing popular legislation while the Dems controlled Congress (just like Obama, 2009-2011). And failed to nominate someone who could have helped reshape the Supreme Court: Mario Cuomo. Democrats in the state legislatures, either thru elected officials or voter-approved initiatives keep cutting their own throats with term limit laws and handing over redistricting to "citizen commissions" whereas Republicans in Red States continued to play hard ball.

Then Democrats lost about 1,000 Congressional, state legislative seats and governorships from 2008 until Obama left office in 2016. And who did they lose them to? Republicans who were generally more radical than those elected in 1994.

Democrats have a leadership problem in Congress, especially in the Senate. That is evident by the W-L record. But the seeds leadings to many of those losses were planted in the state legislatures. Democrats should have gerrymandered House seats in California and New York like Republicans have done in Florida and Texas. Instead, they chose unilateral disarament.

It is an interesting read, but I assume it is of your making. You seem to think that moving social needs by one party was an attack on democracy. Empathy is not anti-democratic! We were moving to a more accepting society, that is not antidemocratic.

What I really do not understand is how radicalization actually occurs. Throughout history there has always been a group that manages to gain acceptance by a group that causes real trouble. Thos current generation has its MAGA. Yes, I worry how this will all end.