Compared with the ongoing firestorm over Russia and impending showdown over health care, President Trump’s meeting with Congressional Black Caucus leaders Wednesday might seem peripheral to a presidency careening through constant turmoil. But the session, which aired but didn’t resolve differences about the federal budget and other domestic issues, captured a critical test of his political movement’s long-term viability.

One of Trump’s most frequently expressed goals is reconstructing the GOP as a “worker’s party” that appeals to blue-collar Americans across racial lines. Key Trump supporters recognize that building an enduring coalition will depend on attracting more working-class black, Hispanic, and other minority voters to the agenda of economic nationalism that has riveted their white counterparts.

“If eight years from now, the Trump agenda ... is only a white majority and it is hanging on by the skin of its teeth, because they are getting 29 percent of the Latino vote and 8 percent of the African American vote, it’s failed,” said Henry Olsen, a senior fellow at the conservative Ethics and Public Policy Center, who has broadly supported Trump’s vision.

Even Stephen Bannon, President Trump’s senior strategist, has implicitly accepted that conclusion. In a revealing post-election interview with The Hollywood Reporter, Bannon put minorities center-stage in his long-term goals. “If we deliver,” Bannon said, “we’ll get 60 percent of the white vote and 40 percent of the black and Hispanic vote, and we’ll govern for 50 years.” With those comments, Bannon effectively conceded that to secure a lasting GOP advantage, Trump needed not only big numbers among whites but also much greater inroads among non-whites.

The force of demographic change largely explains why. Trump last November carried a crushing two-thirds of white voters without a college education—exactly as much as Ronald Reagan in his 1984 landslide and more than any Republican in between. But while Reagan’s dominance among blue-collar whites won him nearly 59 percent of the popular vote, it brought Trump just 46 percent; Reagan swept 525 Electoral College votes, Trump 306.

That erosion reflects two critical changes, each of which pressures Trump to attract more minorities. One is that the number of working-class whites—the group most drawn to Trump—has steadily declined. They constituted nearly two-thirds of all voters in 1984 but just over one-third in 2016, according to media exit polls. (The Census Bureau surveys that provide an alternative measure of voter demographics have put blue-collar whites at slightly above 40 percent, but show the same decades-long decline.) The second change is that Trump’s bellicose nationalism provokes much greater resistance than Reagan faced among college-educated whites, whose numbers have steadily increased since the 1980s. Reagan carried those white-collar whites by 24 percentage points, Trump by just three.

In office, Trump has continued to sharply divide whites along the diploma line. Figures provided by Gallup show that in an average of their daily tracking poll from mid-February to mid-March, a robust three-fifths of whites without a college degree approved of Trump’s job performance, compared with just two-fifths of whites with such a degree. That’s much less support than Republicans usually draw from college-educated whites, and a central reason his overall approval numbers are so unusually low.

Over time, a Trump-style GOP will likely need more backing from working-class minorities to offset both the entrenched resistance from white-collar whites and working-class whites’ inexorable contraction in the electorate. But so far, Trump has posted little progress among blue-collar black or Hispanic voters. In 2016, according to exit polls, Trump drew just under 30 percent from both college- and non-college-educated Hispanics, and won only 7 percent of non-college-educated African Americans. (That’s even slightly less than his 10 percent showing among blacks with degrees.) The Gallup tracking-poll average through mid-March found him drawing positive job ratings from only about one in six non-college-educated African Americans and just one in five Hispanics without degrees.

Veteran Democratic pollster Stanley Greenberg, though, found a larger potential opening for Trump’s message when he gathered focus groups to watch the president’s congressional address in late February. Greenberg, who convened the groups for the liberal organization Women’s Voices Women Vote Action Fund, found that minorities listening to the speech emerged significantly more open to Trump.

In those groups, minorities responded best to Trump’s promises to break the cycle of poverty, reform education, and sustain NATO. Other polls suggest Trump’s tough talk about limiting imports and legal immigration, overhauling education, and rebuilding infrastructure resonate with some minority voters who fear eroding economic opportunity.

But minorities in Greenberg’s focus groups recoiled from Trump’s pledges to repeal the Affordable Care Act and build a border wall. Those reactions capture the barriers Trump faces. His determination to retrench government programs—apart from entitlements benefiting the mostly white senior population—threatens the interests of many minorities, particularly those without advanced education he hopes to court. Nearly 90 percent of the 8.95 million non-whites who gained health insurance under the ACA, for instance, lack college degrees, the Urban Institute found. And the racially barbed edge to Trump’s language—and agenda—on crime and undocumented immigrants creates an even greater obstacle for him with minority voters at all education levels. “Those are inherent problems [for Trump],” Greenberg said.

Trump could squeeze out reelection in 2020 without advancing among minority voters, particularly because demographic change has come more slowly to the Rustbelt states he relies on most. But as Republican pollster Whit Ayres noted in an interview, Trump’s “coalition alone extended out 10 or 15 years is not sufficient to continue to win the presidency.” Trump’s standing with minority voters may offer the most revealing measure of whether he’s reconfiguring the electorate along a new class-based fault line that will lastingly advantage the GOP. Or whether he’s lashing his party to a white identity politics that will steadily sink beneath the waves of irreversible demographic change.