The comparison is apt because he was the last President who committed crimes while in office that would rise to the level of impeachable offense in a non-partisan weighing of fact.
I agree with your assessment of the Republican party - but the party representation reflects the will of Republicans - Republicans voted these candidates into office.
How did this come to pass? How is it that Republicans now support amoral, mendacious - and in some cases - criminals or would-be criminals? What happened to the centrist Republican? Are centrists still the majority but they're going to vote Republican because they always have? Or has America changed since the 1970's - and the centrist Republican is a rare species.
The state of the Republican party is due to a complex confluence of many events, and it's not just Trump.
To answer my own question...
After some thought I think that rural Americans have, for generations, been very suspicious of government and distrustful of legacy media - by which I mean TV broadcasts over air, before even cable was available, consisting of ABC, NBC and CBS. Rural Americans moreover tended to be religious - and even if not religious were very conservative. Moreover, many of them were either slightly racist or very racist, and almost none of them were favorably disposed towards non-heterosexual relations, even those who weren't religious.
Rural Americans in decades past got their news from newspapers and from the big three broadcasters which reported the news factually albeit with a left-leaning bias.
Hence when Nixon was impeached, Republicans writ large were outraged.
Fast forward to the present era - so-called news broadcasts are available from numerous sources. Moreover, Fox News has emerged for aging luddites stuck in the cable news era. Now, rural Americans - as indeed everyone - can watch news or so-called news broadcasts that perfectly mesh with their sentiments. This reinforces their ideas as truthful even if ridiculously counter-factual.
And thus, Trump's failings are easily dismissed as either untruthful, made-up left wing attacks, or as momentary lapses of judgement not reflective of his true character.
Can Democracy in America survive given the status quo in free speech - where one is free to lie about most things - lawsuits seem to be the only curb - free of consequence? In which, basically 1/2 of Americans are tuned into a false narrative?
And honestly, I think that most Republican voters don't frankly care what's true. They've been indoctrinated into an us-versus-them mentality where calamity is just around the corner unless they vote Republican.
TL/DR - The state of the Republican party, I think is due to the widespread availability of so-called news outlets - which allow one to watch broadcasts that reinforce ones viewpoint regardless of fact. It's a Goddamn mess. Even if Trump loses in 2024, it's not over. Come 2028 some new Trump will emerge and we'll be right back at the present - where Democracy is on the line.
And I don't buy for a second all the demographics ideas about young voters replacing older voters and immigrants being more likely to vote Democrat and thus demographics doom Republicans. I've heard precisely this in 1978 from my social studies teacher. Too many factors are at play to confidently predict that the far Right viewpoint in America is dying.