In “Ideological Heterogeneity and the Rise of Donald Trump,” Carmines, Ensley and Wagner make the case that in addition to the classic division of the electorate into three categories — liberal, moderate and conservative — at least two more are needed, populist and libertarian, and perhaps a sixth, nationalist:

Trump’s support among Republican primary voters, and probably in the broader electorate, only makes sense once we recognize that the political choices offered by a conservative Republican Party and a liberal Democratic Party do not reflect the full extent of the ideological heterogeneity found in the American public.

The three argue that by

strategic design or dumb luck, the Trump candidacy was able to activate a segment of the electorate that has historically not been part of the GOP electoral coalition.

These voters, white populists, are citizens with “heterodox policy preferences,” those “who have liberal positions on economic issues and conservative preferences on social issues.” They cut across the traditional left-right divide.

These voters stand out in two important ways. First, they hold what the authors call stronger “nationalist” views, which helps explain their attraction to Trump. These views include the belief that immigration takes jobs, opposition to outsourcing, support for torture and the belief that “blacks have too much influence.”

The three conclude that the ability of the Republicans to mobilize and keep a grip on these voters is a crucial question looking toward future elections:

Trump’s message may have appealed to populists in a way that could have fundamentally altered the electorate in states where white populists reside – states like Wisconsin, Pennsylvania and Michigan. We look forward to finding out.

There are those who see the developments in the American electorate in more evolutionary, less abrupt, terms.

Gary Jacobson, a political scientist at the University of California-San Diego, for example, wrote in an email:

As for Trump reshaping the Republican electorate, it’s more a matter of continuing trends that go back to the 1960s (remember Nixon’s “hard hats,” the white working class “Reagan Democrats”?). As Democrats have become the party of younger, secular, urban, minority, highly educated voters, Republicans have become the party of lower educated whites, religious, conservatives, xenophobes, etc.

Larry Sabato, a political scientist at the University of Virginia, wrote in an email:

Trump reshaped the Republican electorate in 2016, but his performance will determine whether this was a one-shot reshuffling or something more lasting.

The key constituency, Sabato said, is the “slice of non-college-educated white blue-collar workers from cities and older suburbs” who are the “Obama-Trump voters.” In 2016, 209 of the 676 counties that cast majorities for Obama in both 2008 and 2012 backed Trump, many in the Midwest. Sabato noted that it was these voters who “put Trump over the top in Michigan and possibly Wisconsin and Pennsylvania.”

“Those ex-Obama supporters?” Sabato asked:

If Trump produces, they’ll reward him with a second term. If he doesn’t — and he needs to create lots of high-paying jobs in the face of automation and a global economy moving in other directions — then they’ll be ripe for a return to their former home, the Democratic Party — if Democrats give them an appealing nominee.

Alan Abramowitz, a political scientist at Emory, emphasized to me that

white working-class voters have been trending Republican for a long time and white voters with college degrees or post-college education have been trending Democratic as well.

These developments, according to Abramowitz, reflect

an ideological divide over cultural issues and racial issues that has been there for many years. What Trump has done, I think, is put more weight on the racial issues than we have seen before.

Abramowitz emphasizes a key point:

Republican voters are much more conservative on racial issues than in the past while Democratic voters are more liberal on those issues than in the past.

In fact, Trump’s impact on voting patterns was not to increase the share of the white vote won by the Republican presidential candidate. Both Trump and Mitt Romney carried whites by the same 20-point margin.

The big shift Trump wrought was to change the type of whites who voted Republican.

From 1948, when American National Election Studies began polling, to 1964, college-educated voters were decisively Republican and those with high school degrees or less were reliably Democratic. In 1960, for example, voters with high school degrees or less voted 54-46 for John F. Kennedy while those with college and postgraduate degrees voted 62-38 for Richard Nixon.