Trumps entire “platform” (for lack of a better word) is tone deaf grenade-lobbing, so he can no more succeed without it than with it: He HAS nothing else, so MUST continue. That guarantees that sooner or later (probably the first) he will say something that reminds even HIS mindless base he is just a blue blood Yankee robber baron would could not redress their resentments even if inclined, because they fail the Trump Get Rich Quick scheme at Step 1: Get billionaire parents. Whether that moment has already come is impossible to know, and will remain so until it becomes undeniable, but it is inevitable. He did not take a commanding polling lead by wearing a muzzle, so cannot keep it that way.

Most GOP voters could not care less about Latinos except when shipping them back to Mexico (whether or not they actually CAME from there) and his comments on McCain were excused by no less than Rush Limbaugh, whom most Republicans like and respect FAR more than they do McCain. Whether the Megyn Kelly incident will be any different remains to be seen; most of Trumps base is Tea Party, which, as some have noted, hates the GOP establishment (including the Nixon speech writer who founded Faux "News" as its propaganda arm) only slightly less than they hate Dems.

It DOES give Republicans an interesting and desperately needed chance to bash Trump for treating one of their subservient Barbie dolls as they treat all OTHER women. That may give them some cover in their War on Women: "We defended ONE of ya'll (i.e. us) from Trumps sexism, so you chicks are cool now, right? " The latest polls show it has had little or no effect on his numbers, but those polls are all from immediately after the debate, when the consensus was that Fox commentators came after him and he stood his ground: Tomorrows will begin showing the effects of Fox channeling Hillarys War on Women strategy 24/7 since then.

His nomination would hurt far more, for the reason you note: Hillary (or some other Dem if she is indicted, the only way she will not be nominated) would win either way, but the party would not be tainted and accountable for an independent Trump run; if the party CHOSE his offensive jingoism it would be forced to live with the dire consequences long after he is gone. On the other hand, Republicans barely needed five years to come back from Nixon Shock, the Energy Crisis and Watergate, mainly by blaming Carter for the first two, so maybe there is the answer. Trump will NEVER be nominated though; the only question is whether a vindictive candidate who describes himself as “thin skinned” follows through on his petulant threat to run as an independent if the GOP does not “treat me nicely,” because Kelly threw down Foxs gauntlet over a week before the debate, and the suddenly very public rift between the GOPs base and establishment has only continued to escalate through those “champions.”

It could (but probably will not) be a GOP Kobayashi Maru: They dare not accept Trump, because belligerent bigotry is far less tenable than when Rove gay-bashed his way to electing Bush governor, and later to re-electing him president, yet the alternative is only slightly better. Historically, the numbers necessary for populists to wrest parties from establishment leaders has allowed them to survive, even thrive, with the insurgents gradually BECOMING the establishment (Dems have periodically re-enacted the cycle at least since Jackson.) The outcome when establishment leaders put down insurgent revolts is less promising; the Whigs collapsed, and splintered Progressive Republicans made Wilson only the second Democratic president since the Civil War, then bolted entirely to the New Deal, ushering in half a century of leftist dominance so great the only Republicans nationally viable were “Democrat-Lite” candidates like Nelson Rockefeller.

On the other hand, and unlike the Whigs and Progressive Republicans, the GOPs far right base has nowhere else to go, and has always obeyed Reagans Eleventh Commandment: Thou shalt not speak evil of fellow Republicans. That has always kept the base in line by default; however much they privately despised Romney and McCain, they went right out and voted for them anyway because Obama was so intolerable. Hillary is no less so; the question is what happens down the road, as demographics continue diminishing the straight male WASP base that is the GOPs sole constituency. The smart play may be to tell the base to stfu and fall back on the tried and true “godless commie” schtick, since most denominations increasingly not only tolerate but accept gays, and both blacks and hispanics are statistically very religiously observant. I do not know where that would leave you as a straight male WASatheist; probably still a Republican, for the same reason the GOP base is going nowhere else, however studiously ignored.

Funny you should put it that way: Had Reagan not broken US unions and pushed previously nonexistent US debt to skyrocketed levels by promising more benefits AND less taxes, then rammed "free" trade down the throat of an unwilling nation, no one would be blaming China or Mexico for anything, and the budget would still be as fiscally responsible as was before (but only until) he took office. On the other hand, no one put a gun to Clintons head and forced him to wrangle votes for and then sign Reagan and Bushs NAFTA and WTO deals, so maybe they are all pigs in a poke. Which is where guys like Perot and Trump come into the picture. Yet they never stay long; with the notable exception of its prohibition plank, the GOP platform was founded on traditional orthodoxy, so defying that is a hopeless path to enduring popularity among Republicans.

EDIT: I must say though, on the long list of laughably unlikely events I would pay money to see, half a year of The Donald v. Bernie is near the top. If Trump lost the US presidency to publicly confessed socialist he would probably jump off the top of a Trump Tower.