The nomination of Donald Trump as the Republican presidential nominee in Cleveland in July, and his possible election in November, will change American politics indelibly.

First of all, it will change the demographics of the Republican Party, lately a party divided between a mainstream conservative establishment and a growing populist conservative grassroots base.

The beginning of this divide took place in 1964, when an "outsider" (Senator Barry Goldwater) won the GOP nomination asserting values and beliefs that were jarring not only to Democrats, but to establishment moderate Republicans, who would have preferred New York Governor Nelson Rockefeller to be their standard-bearer.  Mr. Goldwater then lost badly in November, but his flag was picked up after a politically unfortunate interregnum with Richard Nixon and Spiro Agnew (both of whom finally resigned in disgrace) by Ronald Reagan, a fading movie star who had been elected governor of California.

In 1980, much to the surprise of many observers, Mr. Reagan won the presidency from a hapless one-term incumbent (Jimmy Carter) with the key help of some blue-collar Democrats, and he followed that victory with a landslide in 1984 against Mr. Carter's vice president, Walter Mondale.  He accomplished this with even more blue-collar and middle-class voters who had previously been electing Democrats.

Much as the Democrats and their media allies like to portray Republicans as plutocrats, exploiters of the poor, and religious fanatics, that image is now a half-century or more out of date.  (In fact, most of the new super-rich are liberal voters and donors, and many liberals are for anti-free speech political correctness and are feverishly anti-religious).  Corporate America has been tilting to the Democrats for years, and the party that championed the founding of the state of Israel has now become predominantly (and shamefully) anti-Israel.

Most Republicans today are struggling entrepreneurs, blue-collar and lower-income white-collar workers who hold traditional social values and religious beliefs.  The old upper-income, Ivy League-educated GOP establishment has dwindled, although it has maintained a hold on conservative institutions.

There are divisions within these ranks.  Social conservatives often resist social changes in American society, while "libertarian" conservatives embrace them.  Some conservatives are pro-free trade internationalists; others have U.S. interests as a priority.  There are differences about the use of the military.  The conservative grassroots are not a monolith.

One casualty of this evolution of the Republican Party has been the turning away from a former centrist base that included pro-choice and "moderate" Republicans, sometimes call "RINOs" ("Republicans in name only").  This cleavage paralleled an equivalent cleavage on the Democrat side, in which "pro-life" and traditionally religious centrist liberals were systematically drummed out of the party.

Donald Trump's emergence turns this upside-down.  A former liberal Democrat (as was Ronald Reagan), super-rich, educated at a top Ivy League university, Trump nonetheless speaks the language of the new class of Republican conservative grassroots voters.  He annoys, with that same language, the old establishment political class of the GOP, who have for years now enjoyed the votes of the new class but ignored their concerns, anxieties, and aspirations.

Although I did not at all see the Trump phenomenon coming, and he was not my preferred candidate for president in 2016, I now see what I have described in recent months as a "mutiny" of voters.  The working crews of the Republican and Democratic Parties have risen up against the captains and officers.  In the case of the Democrats, the mutiny has been partly put down for the time being, but in the case of the Republicans, the mutiny is succeeding, with a stowaway named Donald Trump as the new captain.

It is a self-delusion for the old GOP mainstream to believe that Mr. Trump is destined to lose the 2016 election and that all will revert back to normal in the Republican Party after that election.  The columnist George Will personifies this kind of thinking.  He calls any conservative who supports Mr. Trump a "quisling" – a term derived from the name of a Norwegian fascist politician who became the puppet leader of that nation under Hitlerian control during World War II.  Mr. Will, who for years has picked losers to be nominees of the Republican Party, typifies the snobbery that has alienated so many grassroots conservatives.  Mr. Will is a bright, articulate, and often thoughtful essayist on public policy issues, and I often agree with his views but not his elitist disdain for anyone who disagrees with him.

There has been a mean side to Donald Trump's discourse in the 2016 campaign, including three among many instances: his put-down of Marco Rubio as "little Marco," his denigration of John McCain's distinguished war service, and his completely wrong and mean-spirited description of Tom Ridge as a "failed Pennsylvania governor."  (Mr. Ridge was probably the most accomplished chief executive of the Keystone State in the post-war period.)  Some of Trump's language about women was not merely politically incorrect, but plain crude and sexist.  Most observers, myself included, put a focus on this, and not on the larger strategy Donald Trump was pursuing this campaign year, and we missed the connection the New York businessman was making with the Republican grassroots on other issues.

If Donald Trump the GOP nominee is merely a duplicate of Donald Trump the nomination aspirant, he will likely fail in November.  Knowing his experience and his ego, I think that is unlikely, but should he fail to be elected president, the republic will survive.

The Republican Party, on the other hand, will not be the same whether Mr. Trump wins or loses.  A new generation and a new class of conservatives have taken over the ship (as has also happened in the Democratic Party), and from now on (as far as we can see on the political horizon), it will not ever again be politics as has been usual in the USA.