How did the Republican Party get into this fix?

I seem to be writing more about the American presidential nominations than anything else at the moment, but it is undeniably fascinating, albeit in much the same way as a slow-motion train crash is fascinating.
To read the thinking media, particularly the Canadian media, one gets the impresssion that almost everyone, including what is usually referred to as the "traditional" wing or the "establishment" of the Republican Party, is against Donald Trump achieving control of the GOP.
Attitudes range from distaste to indignation to outright fear or incomprehension. But hardly anyone has a good word to say about the man, save a few fellow outliers like Sarah Palin and Chris Christie. And yet, Mr. Trump remains far and away the candidate to catch in the Republican nomination primaries.
So, how does that work? Who are these people who are in the process of voting Trump into a position of huge power and influence?
A brief perusal of the Vote Smart Government 101 web page on presidential primaries reveals that this is actually far from simple, and varies significantly from state to state. Some states use a caucus systems, most use primaries, some even use a hybrid of the two; some of these primaries may be closed, some open, some blanket; some ballots show the candidate's name, some just the name of a delegate who may or may not represent a candidate; some states award delegates on a winner-takes-all basis, some on a proportional basis. Quite honestly, it is a bureaucratic nightmare of a system, making results almost impossible to predict, and, in my view, rendering the whole thing of frankly dubious democratic value.
But the short answer to the question is that the people voting for Trump are Republican voters who have registered with the party, essentially party members. Of course, even how to become a registered voter seems to vary from state to state, but typically it is not particularly onerous and does not cost any money, so any Tom, Dick or Harry with a political bent can get themselves a vote in the process, which I guess is all as it should be.
But these people seem to be distinctly at odds with "establishment" Republicans. There are signs that many stalwart Republicans will actually vote Democratic for the first time ever rather than vote for the GOP with Trump at the helm, fully realizing that this may hand Hillary Clinton the presidency, and even swing the Supreme Court membership towards the Democrats for years to come. They would prefer to vote against the Republican Party than to vote for Donald Trump - there ia a whole movement building under the Twitter hashtag #NeverTrump - and many would admit that the GOP as a whole is in some kind of existential crisis or limbo at the moment.
Why, then, are so many willing to vote for Trump, despite his obvious failings in some of the most important requirements of the job, and despite repeated warnings from prominent Republicans and media outlets?
This is not easy to answer, partly because Mr. Trump's support does not necessarily follow logic. For example, it turns out that Donald Trump is the candidate of choice among Muslim Republicans, despite his prominent anti-Muslim platform! Indeed, if you read some of the reasons people give for supporting Trump, most of them make very little sense, or at least bear little relationship to reality (many of these people are, I fear, not particularly well-educated).
But what comes through most is a general feeling of disillusionment with the status quo, an impatience with political correctness in all its forms, a bold defiance of orthodoxy (to a fault), an underlying fear of immigration and diversity in general, and an undercurrent of respect for a self-made businessman (whatever you might think of Trump's achievements in that area). He represents for many the image of a strong, authoritarian figure, one that is willing to tell it like it is, in simplistic terms, and without concern either for anyone who might be offended, or for his own political masters. That may be all there is to it; policies and thought processes are very much secondary, or even just plain redundant.
Trump supporters tend to be relatively poorly-educated, working class, white, male and older, people who feel they have been let down and left behind by the new realities of 21st century, multi-racial progressive America in a globalized world. Paradoxically, these people would be better served by the Democratic Party, which is committed to reducing income inequality, expanding healthcare, etc. But, crucially, these are people whose deep-seated racism and nativism outweighs more logical economic and political reasoning. Mr. Trump is the only "mainstream" politician willing to pander to these instincts.
Whatever your opinion of Donald Trump, these are heady days indeed for political pundits, and the Internet is a-buzz with comments of all political stripes, some guarded, some not so much. But it remains to be seen how the whole thing - both the nominations, and the subsequent presidential vote - will play out. Who knows, it may have the very positive effect of a short sharp shock to wake up the American electorate, but let's all hope that we don't have to actually live through a Trump presidency for that effect to become apparent.