THE Republican establishment typically has a dependable ally in the primaries: the blue-state Republicans. They’re relatively affluent, well educated, moderate and secular, which usually makes them a natural partner to offset the more populist, religious and conservative outsider candidates who often rally the party’s Southern base.
But this year, blue-state Republicans have abandoned the establishment for Donald J. Trump. So far, Mr. Trump has won every non-caucus contest in a state carried by Barack Obama in 2012, with the exception of John Kasich’s home state, Ohio. Mr. Trump is expected to win in California and along the Acela Corridor, which vote in the second half of the primary season. If he eventually gets a majority of delegates to the Republican convention, it will be because of the 15 or so most reliably Democratic states.
But Mr. Trump’s blue-state appeal is a little hard to explain. It’s well established that he fares best among less educated voters. Yet his strongest performance so far wasn’t in Mississippi, where he got 47 percent of the Republican vote, but in Massachusetts, a famously liberal state, where he won 49 percent of Republican voters.
His appeal in historically Democratic areas is a reflection of strength among new Republicans — whether they be white Southerners or white Roman Catholics and working-class voters in the North who would have had no place in the Republican Party a half-century ago.
Mr. Trump’s strength among those voters, who decades ago represented the base of the Democratic Party, helps explain the resilience of his candidacy. It’s no surprise that they are not offended by his unorthodox policy views, like his embrace of entitlement programs or his opposition to free trade. They may have moved to the Republican side, but they still have moderate views on economics.
There is evidence both anecdotal and statistical that racism was another factor in the shift of some of these voters to the Republican Party. And that helps explain why he’s withstood controversy after controversy over racially charged remarks.
Mr. Trump’s success is the culmination of electoral changes that have erased and even reversed the political divides of the post-Civil War and New Deal eras. Today, Republicans draw more than two-thirds of white Southern voters, and nearly three-quarters of white Southerners outside Florida and Virginia. They win nearly two-thirds of white voters without a college degree. They even win white Catholics in the Northeast and Midwest.
Early in the campaign, Marco Rubio warned that “the party of Lincoln is on the verge of being taken over by a con artist.” In a sense, the party of Lincoln is on the verge of being taken over by the voters of Stephen Douglas and George C. Wallace.
Many of these voters have been voting Republican in presidential elections for years or even decades. For that reason, Mr. Trump’s strength among them may not augur any great risk to the Democratic nominee in the general election.
But they’re not typical Republican primary voters, either — they may not even consider themselves Republicans. Mr. Trump fares best among people who identify as Republicans but nonetheless remain registered Democrats or have a history of voting in Democratic primaries — a legacy of their previous political allegiances — according to data from Civis Analytics, a Democratic firm.
One result is that Mr. Trump’s strength mirrors that of the Democrats in the middle part of the last century. It may seem odd to see Massachusetts paired with Mississippi as the top two states for Mr. Trump, but it’s something the Democrats pulled off quite regularly from 1928 until the passage of the Civil Rights Act.
Take Massachusetts, where Catholics made up a majority of the Republican electorate and provided Mr. Trump with a big primary victory. He drew 53 percent of Catholics in the Massachusetts G.O.P. primary, while Mr. Kasich and Mr. Rubio combined for just 35 percent. The story was the opposite among mainline Protestants — the traditional Republicans — who supported Mr. Kasich and Mr. Rubio over Mr. Trump.
There’s more to Mr. Trump’s advantage in the blue states than the new Republicans. His main opponent, Ted Cruz, fares best among voters of the religious right who identify in polls as “very conservative,” which makes him a bad fit for the more moderate blue states.
But Mr. Trump’s weak opposition is in part a product of his own strength in the blue states. It helped block the emergence of a mainstream candidate, like Jeb Bush, leaving conservative states to elevate Mr. Cruz, a candidate with little appeal to the blue states, as Mr. Trump’s principal rival.
The less religious Republican voters in the Northeast might be a factor in Mr. Trump’s strength as well. Mr. Trump does worst in areas with high church attendance, like Western Michigan or Utah. When he draws voters who are both working class and less religious — as in Massachusetts — he can really run up the score.
Another important factor is race. So far, there has been a strong relationship between Mr. Trump’s share of the vote by state and measures of racial animosity or bias. While no one suggests that all of Mr. Trump’s supporters are racist, surveys show that they are particularly likely to express explicit racial prejudice. And the Northeastern states often sit alongside the South at the top of these indicators, despite the Northeast’s reputation as a bastion of liberalism.
There’s a remarkably strong correlation, for example, between Mr. Trump’s support and the number of racist Web searches by state. Nate Silver of FiveThirtyEight said that the measure was the single strongest correlation of support for Mr. Trump that he could find.
Survey data point toward the same finding. For instance, support for Mr. Trump was strongly correlated with higher levels of resentment about racial issues — like the belief that black people don’t work hard enough and yet receive special favors — in an analysis of the American National Election 2016 Pilot Study.
Mr. Trump’s strength among voters with higher levels of racial resentment helps explain his strength among the new Republicans, many of whom shifted allegiance during moments when race was particularly salient in politics, the 1960s, the 1980s and even during the Obama era.
Of course, not all of the new Republicans left the Democrats because of racial resentment. The Democrats’ leftward shift on other cultural issues — like abortion and gay marriage — undoubtedly alienated many Catholics and Southern Evangelicals. The rising affluence of these same groups most likely diminished the economic appeal of the Democratic message over the last century as well.
But Nixon’s “Southern strategy” had a Northeastern component, and it drew plenty of old Democrats into the Republican Party. In his influential book “The Emerging Republican Majority,” the Nixon adviser Kevin Phillips noted the declining Democratic strength among Northeastern Catholics in the 1960s, in part because of the view that “Negroes or other minority groups are taking over the Democratic Party.” His prediction that the Republican Party would become more Catholic and populist has been borne out.
The trend continued in the 1980s. The term “Reagan Democrat” was coined by the Democratic pollster Stan Greenberg in Macomb County, Mich., where autoworkers saw the Democrats as working for the benefit of minority groups. Mr. Trump won 48 percent of the vote in Macomb County in early March.
A similar pattern resurfaces in 2008, when Hillary Clinton defeated Mr. Obama among white voters across nearly this same area.
It is in the Midwest and West where Mr. Trump has struggled. There, the traditional Republicans — white Protestants — still reign. They have bled support to the Democrats in many places, like Iowa or Oregon, but the Republicans have not replaced them with an influx of new voters as they have in the South or the industrial North.
And those who remain in the party have not taken to Mr. Trump. Perhaps it’s just that the region posts far lower scores on measures of racial animus.
Or maybe it’s just because these are traditional Republican voters, with traditional conservative values.