MIAMI—Donald Trump has advanced to the brink of the Republican presidential nomination not by transforming the GOP electorate, but by dividing it along a new axis.

Though some conservative Trump critics have claimed that he has relied on a surge of non-Republican voters, the exit polls conducted so far in 15 states point toward the opposite conclusion. Overall, although turnout has soared from 2012, the share of the total primary votes cast by self-identified Republicans this year is virtually unchanged. And Trump has beaten his rivals among self-identified Republicans in every exit poll conducted in states that he has won.

Together these patterns suggest that Trump has built his coalition primarily from voters within the heart of the Republican electorate—a dynamic that could make it more difficult for the party leaders to deny him the nomination if he finishes the primaries with the most delegates, but less than an absolute majority. It also suggests that his rise could signal a lasting shift in the party’s balance of power toward the anti-establishment, heavily blue-collar voters who have provided the core of his support.

Trump’s consistent success with those voters has replaced many of the party’s traditional divides—such as religious identification and ideology—with a new fissure centered on class and alienation from institutions. In that sense, Trump this year has been as much a demand-side as a supply-side phenomenon. He is coalescing, and giving voice to, an increasingly important component of the existing Republican coalition—one that earlier blue-collar populists such as Patrick J. Buchanan in 1996 and Rick Santorum in 2012 also tried to mobilize, with much less success.

“It is a part of the coalition that has always been there,” adds Alan Abramowitz, an Emory University political scientist. “It’s just that he’s capitalizing on this anti-establishment anger within the party, that’s been directed toward the Democrats and President Obama, now he’s directing it inward. And the key issues he talks about, the nativist appeal that he has, is broadly popular among Republican voters.”

Turnout in the GOP race this year has soared, compared to 2012, as Trump has frequently noted. In the states that have voted so far, turnout is up by 4.5 million in the Republican contests compared to 2012, or 61 percent, according to a compilation by Public Opinion Strategies, a GOP public-opinion firm.

But while turnout has increased, the composition of the vote has not significantly changed, exit polls have found. Trump has noted reports in several states of Democrats switching their registration to participate in primaries. “We're taking people from the Democrat Party,” he said at the Republican debate here Thursday. “We're taking people as independents, and they're all coming out and the whole world is talking about it. It's very exciting. I think, frankly, the Republican establishment, or whatever you want to call it, should embrace what's happening.”

But exit polls conducted in 15 states so far do not show that the Republican electorate has been meaningfully changed by a surge of independent and Democratic voters. In eight of the 15 states, the share of the vote cast by self-identified Republicans has actually increased since 2012, the exit polls found. In two more states, the share of the vote cast by Republicans has declined by just one or two percentage points. Only in five states has the share of the vote cast by Republicans dropped by at least three percentage points. The biggest decline (eight percentage points) came in Texas, which Ted Cruz carried. The other largest declines came in four Southern states—Arkansas, Georgia, Tennessee, and Mississippi—that Trump won.

Using a statistical technique to cumulate the results from all 15 exit polls, Public Opinion Strategies calculated this week that self-identified Republicans have cast 67 percent of the votes through the entire GOP primary this year. That’s virtually unchanged from 68 percent in 2012. Democrats have cast four percent of the votes in GOP primaries so far, unchanged from 2012. Among independents, the share of the vote has increased minimally from 28 percent in 2008 to 29 percent last time.  That suggests while Trump can legitimately claim credit for increasing participation, he appears to be turning out Republican-leaning voters who did not vote in the 2012 primaries, and perhaps earlier too. “I think what Trump has been able to do is not so much change the composition of the electorate but just grow it,” said Republican pollster Glen Bolger. “And obviously he got a bunch of people excited about voting, either for him or against him.”

The pattern of Trump’s support also undermines the idea that he has significantly relied on voters outside of the Republican coalition. Trump has captured 12 of the 15 states in which exit polls have been conducted. In all 12 of those states, Trump has led all of his rivals among voters who identified as Republicans. In none of those states has Trump drawn a significantly higher share of the vote among independents than he did among Republicans. In Georgia, New Hampshire, Tennessee, and Mississippi he won exactly the same share of the vote with both groups. And when the two groups diverged, Trump frequently won a higher share of the vote among Republicans than independents—as he did in Virginia, Alabama, and Vermont.

Rather than relying on independents or Democratic crossovers, Trump has accelerated away from his rivals by dominating them among Republican voters without a college degree, while remaining competitive among the party’s white-collar wing.

Those white working-class voters have not increased as a share of the overall vote: While voters with less than a four-year college degree constituted 51 percent of Republican primary voters in 2012, that has dipped slightly to 47 percent this year, according to the Public Opinion Strategies compilation.

But they have provided Trump an impenetrable foundation of support. Trump, according to the exit polls, has carried white voters without a college degree in 12 of the 15 states with exit polls, losing them only to Cruz in Oklahoma, Texas, and Iowa, three states that the Texas senator carried. Even in a crowded multi-candidate field, Trump has carried half or more of those non-college whites in Massachusetts, Mississippi, Alabama, and Nevada; between 42 and 47 percent in Georgia, Virginia, Tennessee, Michigan, New Hampshire, and South Carolina; and 39 percent of them in both Arkansas and Vermont.

Trump’s strength among those voters—who combine economic strain, cultural anxiety and hostility to elites—has remained constant almost everywhere. That has allowed him to compete across the geographic divides that stymied the previous two Republican nominees, Mitt Romney and John McCain. Trump demonstrated much broader geographic reach than either of them on Super Tuesday when he simultaneously carried Vermont and Massachusetts on the one hand, and Arkansas and Alabama on the other, then reinforced the message this week by triumphing in Michigan and Mississippi on the same night.

“It’s not the where, it’s the who,” says Bolger, who has been critical of Trump but is unaffiliated in the race. “Support for Trump is all about the lack of trust in institutions, whether it’s Congress, the presidency, the Republican Party, Wall Street, the banks. He is the one guy who can thumb his nose at institutions, which is what his voters want to do as well. The rules of previous elections, about geography, are thrown out the window. He is appealing to a significant group of voters who have never coalesced this significantly across the country behind a candidate.”

These resounding results indicate that Trump has succeeded in progressing far beyond the beachhead established by Buchanan in 1996 and Santorum in 2012. Each of them had also tried to mobilize blue-collar Republicans around an insular message of protectionism and skepticism of immigration similar to Trump’s but with a much higher quotient of cultural conservatism. Neither, however, garnered nearly as much attention, or mobilized nearly as much support, as Trump has done.

“Four years later, two things have happened that have created an incendiary thing,” says John Brabender, Santorum’s chief strategist in 2012. “[These voters] are madder than all heck, much more than they were four years ago. And Donald Trump has a much bigger megaphone than Rick Santorum ever had. And there is a badge of honor among them that they are changing history in some sense. This is where a lot of the party types aren’t understanding why trotting out Mitt Romney [to criticize Trump] isn’t having a bigger impact than they were hoping. It is solidifying for these people that they are charting a new course [for the party].”

By contrast, another candidate has topped Trump among white voters with at least a four year-college degree in Iowa, South Carolina, Arkansas, Oklahoma and Virginia (Rubio); Texas (Cruz); and Vermont and Michigan (Kasich). Trump’s share of the vote among college-educated Republicans has reached 40 percent only in four states (Mississippi, Massachusetts Georgia, and Nevada) and dipped below 30 percent in five states. His vote has fallen that low among non-college whites only in the first state, Iowa, when he drew 27 percent in a very crowded field.

Critically, Trump’s advantage among blue-collar whites has extended to those are also evangelical Christians. Both in 2008 and 2012, there was no significant difference in the voting patterns of evangelicals with and without college degrees, exit polls found. Instead, the key difference were whether voters were evangelicals or not: Both John McCain in 2008 and Mitt Romney four years later ran much better with the latter than the former.

This year, Trump has carried evangelicals without a college degree in nine of the 13 states with enough of them to measure, and tied with Cruz among them in a tenth, according to exit-poll analysis conducted by the CNN polling unit. Trump has made much more modest inroads among evangelicals holding a four-year degree or more: He’s carried them in five states, compared to six for Cruz and two for Rubio.

Yet for all of these advances, Trump has won only a combined 35 percent of the total votes cast in the contests held through this Tuesday, according to the Public Opinion Strategies compilation. That puts him six percentage points ahead of Cruz, who has won 29 percent. Trump’s vote has exceeded 40 percent in only six of the 24 states that have voted, with Massachusetts at 49 percent, the high point. (Exit polls have not been conducted in all states.)

Earlier leaders like McCain and Romney have seen both voters and elected officials consolidate around them after early successes: McCain, for instance, drove his last remaining rival Mike Huckabee, from the 2008 race by reaching 50 percent or more in 10 straight contests through late February and early March that year. By comparison, Trump remains a plurality front-runner, facing significant negative ratings even among GOP voters, and rising resistance in recent weeks from party leaders—not to mention a hailstorm of negative poll numbers from the overall public in recent surveys. “He appeals to a certain segment, but not much more than that, because his numbers aren’t growing,” says Bolger.

The front-runner’s inability to consolidate the party more completely is “a legitimate criticism of the Trump campaign,” says Brabender. “The one failure they’ve had is their inability to grow this coalition. They had an opportunity to do that after South Carolina. They could have looked a little more comforting to the establishment side, and looked a little more under control without losing their [base] vote. If I were the Trump people I would be worried about that.”

That resistance will likely provide enough oxygen for at least Cruz, and perhaps others, to continue contesting Trump for weeks to come. But none of Trump’s rivals so far has demonstrated the ability to consistently build a broader coalition than his—or to establish as commanding an advantage with any other group of voters as he has amassed with non-college whites. Though the race will undoubtedly continue, if Trump wins all, or nearly all, of the five big states voting next Tuesday, his Republican revolution from within likely will become impossible to reverse.