Whatever the reason, the last presidential election appears to have destroyed any confidence that the Democrats had in the idea that Republicans are merely misguided.  A currently growing cleavage within the Democratic Party itself cannot hide the fact that virtually all Democrats appear to agree on the idea that Trump is fundamentally evil and that the 63 million people who voted for him are evil for having supported him.

From the very beginning — even before the emergence of a new and powerful strain of progressive ideology within the party — the "resistance" movement was more concerned with rejecting the morality of Republicans than with challenging their policies.  The willingness of the Democrats to boycott Trump's inauguration is evidence of this, as is the enthusiasm for an investigation into his behavior without reference to any specific criminal act.

Of course Trump's policy actions are resisted; this is standard practice by whatever party is out of power.  The point is that the Democrat condemnation of Trump was proclaimed loudly and openly before he was sworn into office.  He was to be impeached even before having done anything.

At that time, those who voted for Trump began to fear that Democrats harbor an abhorrence for them as voters for having elected such an evil person.  The Democrat "resistance" has done little to reason Republicans away from their support for him; instead, it has treated Trump-supporters as willing lackeys in an evil plot.  It increasingly labels them as racist, sexist, homophobic, etc. 

For all their rhetoric about how divisive the president is, it is the Democrats themselves who have forced the grand division by refusing to accept a properly elected president as legitimate.  By focusing on what they fear he might do in the future rather than what he has been doing in the past and present, Democrats have found it appropriate to condemn him in an unqualified and unequivocal manner.  The message for his supporters is clear: "you are willing accomplices to a fascist agenda."

No self-respecting "fascist" is going to accept such slander lying down, and over the past two years, increasing numbers of Trump-supporters who at first were shrinking violets in the face of such Democrat opprobrium have become hardened against such condemnation and shaming and now look upon Trump — the flawed and uncouth warrior — as an exemplar.  In short, Trump has set an example and ever larger numbers of his supporters are now prepared to fight back — not so much because he is always right, but because the Democrats have proven to be traitors to the social contract.  Democrats no longer accept Republicans as having moral integrity, an attitude that with time will destroy the republic.

The great majority of Trump-supporters have come to terms with the fact that the Democrats hate them, and — human nature being what it is — they now view Democrats as deserving of like treatment.  Self-preservation requires that Republicans respond by distrusting Democrats, and we have good logical reasons for embracing such distrust.  Here are a few:

1. The efforts to delegitimize the Trump presidency that started even before he took office.

2. The constant personal attacks on the president himself rather than his policies.

3. The silence regarding anything positive that happens during the Trump presidency.

4. The willingness to undermine the president while he is engaged in foreign affairs.

Above and beyond these telltale behaviors are two watershed events that have done the most to cement a Republican distrust of Democrat motives.  The first is the dishonorable way in which all Democrats attempted to destroy Brett Kavanaugh with no clear evidence that he was guilty of anything.  The words of Senator Lindsey Graham captured the outrage and disgust that Republicans felt regarding Democrat behavior.  Indeed, his condemnation of all Democrat senators on the Senate Judiciary Committee transformed him from a suspect RINO into a conservative hero.

Now we are in the middle of an even greater watershed event that is in the process of hardening Republican distrust of Democrats on a personal level.  The evidence has become irrefutable that the Obama FBI spied on Trump with no solid basis for doing so; that a formal investigation of Trump was undertaken without notifying Congress, as the FBI was legally obliged to do and without notifying Trump himself; that the spying on Trump was effectuated by obtaining a FISA warrant based on a now discredited piece of opposition research assembled by the Clinton campaign; that Clinton was exonerated of documented law-breaking because the Obama Justice Department commanded it; and that the Obama administration illegally orchestrated the selective unmasking of multiple Trump staff members so as to damage the Trump campaign and then the Trump presidency.

The rank-and-file Democrat had nothing to do with these many examples of high crimes and misdemeanors committed by highly placed officials in the Justice Department, the FBI, and even the Obama inner circle, but now that the evidence is out there in plain view, those rank-and-file Democrats have an obligation to condemn the perpetrators.  Until they do, Republicans will condemn them as morally bankrupt.    

Polarization of opinion is historically common.  Whenever a divisive issue seizes the attention of the American public, passionately held views conflict to an alarming degree, and a great gulf opens up between the two sides of the divide.  Recent examples might include the war in Vietnam, the abortion debate, and the question as to whether access to health care is an inalienable right.

Disagreement about these sorts of serious matters is perfectly normal.  Usually, both sides claim to adhere to principled points of view, and their differences arise from the priority that the two parties agree upon moral principles — principles that to a greater or lesser degree they both hold in some regard.  But now the situation is dire: Democrats no longer trust Republicans, and Republicans are rapidly growing to distrust Democrats.  Only if Democrats begin to openly admit that Trump — however bad he may be in their eyes — did not collude with Russia can Republican suspicions regarding their motives be assuaged.  Only if Democrats reluctantly come to terms with the fact that a Democrat administration broke the law will there be any chance of re-establishing public trust in our governmental institutions.