I understand this line of thinking and hear it quite often publicly from people I know and in the media. I'll respond to each point separately:
1) I would argue the "hardening of Trump's support" is not the fault nor responsibility of Democrats or the media which is the other common scapegoat. The hardening is caused by the hatred of the right which includes many Republican party members and Trump voters for anything progressive, forward thinking or inclusive. The Republicans since 1994 have leaned in hard (and even harder since Obama was elected in 2008) to protecting their followers from what they believe is a conspiracy to strip white protestant christians of their rights, their identity and their viability as the ruling cohort of American culture, economics and politics.
This hatred is also combined with the delusion of a winner take all philosophy i.e. if a Democrat wins an election or a gay person is acknowledged as a full citizen or women are given equal pay in the workplace or people of color are treated as legitimate human beings, then all white protestant christians and increasingly Republicans lose out and are that much closer to subjugation.
This is a centuries old fallacy born out of theories of inferior races, the weaker sex and the evil nature of sexual deviants that has been used to justify all kinds of injustice including slavery and beyond.
2) enforcing the rule of law is not "hoisting Trump up as a martyr". That is Republican spin aimed at trying to stop law enforcement from moving forward and scaring people into believing it is too dangerous for our country/system to hold Trump and the Republicans accountable. Call it the political equivalent of "too big to fail" or the main lesson of Jan 6th in some circles. If Trump is convicted and put in prison, the country will plunge into civil war and destroy itself.
Is it possible there might be another Jan 6th or some other type of political riot or coup attempt to save Trump? Could some states attempt to secede from the Union again over this issue? Sure, those are possible, but the chance they would ever succeed is very remote. The vast majority of the country does not support Trump and the ones that do have limited federal power. In our history, we have undergone much more fundamental change than that and come out intact and, in some cases, more united.
Plus, the charges Trump faces are far from trivial. Corrupting an election like Trump and the Republicans did in 2016 not only with these illegal hush money payments, but the campaign coordination with Russian interests the Mueller report documented, the theft and distribution of Democratic party property and the flood of disinformation successful at manipulating the American people is very serious. Trump is facing even more serious charges in Georgia for (again) working to corrupt an election and from the DOJ for the attempted insurrection and handling of classified materials that he could be indicted for any week now. These are violations anyone with any fidelity to the rule of law, justice or a constitutional order can ignore or push aside. It is the sworn duty of our elected officials to enforce and defend these foundational pillars of our Republic.
3) I try hard not to painting any group with a generalizing broad brush. Clinton had already lost due to her own and the party's incompetence when she made the deplorables remark, but it did not help her. I stand behind my belief though that anyone still supporting Trump after everything that has been revealed and by looking at his own actions has either given up on American democracy or never understood it in the first place. They appear to be driven by more base motivations: anger, fear, desperation and religious zeal that turns everything into a good vs evil choice and removes any option to step back, analyze and reconsider their words and deeds or the path they are taking the country down.
I agree Democrats should not be funding extremist candidates to have potentially easier election cycles nor should they be supporting any effort to make sure Trump is the nominee, but I see very little of that happening. Democrats have been among the only ones fighting against Trump and Trumpism for the last 8 years. That seems to likely continue to be the case due to Republicans locking themselves up into strict conformity to Trump. Maybe the Republicans could start pulling on the rope with Democrats like they did with Nixon and we might get somewhere better together.