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In most of America, Donald Trump is polling far behind the last Republican nominee. But one conspicuous exception has been the upper Midwest, where Trump is on pace to win two states Mitt Romney lost — Ohio and Iowa — while proving roughly as competitive as the 2012 standard-bearer in the likely blue states of Wisconsin and Michigan.

On a surface level, the mogul’s strength in this region can be attributed to its abundance of white voters without college diplomas — a demographic that’s been far more forgiving of Trump’s myriad outrages than the college-educated whites who predominate in eastern states like Virginia and North Carolina.

But this analysis just begs the question of why those voters have been so forgiving. Historically, white working-class voters in the Midwest have been far more liberal and Democratic than those in other regions. After all, Obama won Ohio and Iowa with significant white working-class support just four years ago. What did Trump (or Clinton) do to break up that coalition?

Some pundits have argued that Trump’s anti-trade message has resonated in the Rust Belt towns that became “globalization’s losers.” Others have suggested that the GOP nominee’s populist call for change mobilized whites in rural enclaves that the recovery has left behind. And there are certainly Trump supporters who fit both of these narratives.

But a new demographic analysis from The Wall Street Journal suggests Trump’s popularity in the heartland is actually driven by the region’s booming diversity.

When you think about America as a multicultural melting pot, you probably don’t picture small towns in the upper Midwest — and neither did their longtime white residents, until recently. But between 2000 and 2015, the diversity index — a measure of the chance that any two people in an area will have a different race or ethnicity — doubled in 244 counties in the United States, more than half of which were clustered in five midwestern states. Per the Journal:

[C]ensus data shows that counties in a distinct cluster of Midwestern states—Iowa, Indiana, Wisconsin, Illinois and Minnesota—saw among the fastest influxes of nonwhite residents of anywhere in the U.S. between 2000 and 2015. Hundreds of cities long dominated by white residents got a burst of Latino newcomers who migrated from Central America or uprooted from California and Texas



… In 88% of the rapidly diversifying counties, Latino population growth was the main driver … Mr. Trump won about 71% of sizable counties nationwide during the Republican presidential primaries. He took 73% of those where diversity at least doubled since 2000, and 80% of those where the diversity index rose at least 150%, the Journal’s analysis found.

The most convincing research I've seen decoupling economic anxiety from cultural/racial anxiety & support for Trump. https://t.co/lv9XRxIfKc pic.twitter.com/h9BfiV8PT4 — Noah Rothman (@NoahCRothman) November 1, 2016

Notably, rapid diversification was correlated with low unemployment rates. Which makes sense: Immigrants tend to move in the direction of job opportunities. However, the fact that Trump support is especially strong in areas with low unemployment and a lot of new immigrants suggests that many of his backers are animated by anxieties more cultural than economic.

That said, local unemployment rates aren’t the only measure of an area’s economic well-being. And to the extent that new arrivals are disproportionately less prosperous than the preexisting population, a rapid influx of immigrants can pose some genuine material challenges to a municipality. In the Journal’s case study — Arcadia, Wisconsin — the Hispanic share of the population jumped from 3 percent in 2000 to 35 percent in 2014. This year, the share of students who qualify for free or reduced-price lunch rose to 65 percent, up from 20 percent in the late 1990s. And the need to expand ESL programs has required shifting some education spending away from the children of longtime residents and toward those of new arrivals.

But then immigrants have also increased the economic growth and tax base of Arcadia, solving the town’s labor deficit and allowing its furniture company to thrive. In turn, that furniture company has reinvested in the town, financing the construction of soccer fields and basketball courts.

And the political backlash to the town’s demographic change has often centered on cultural complaints. In 2006, Arcadia’s then-mayor called for making English the exclusive language on directional signage and making it illegal to publicly display a foreign flag without accompanying the banner with an American one.

Regardless, the correlation between rapid diversification and Trump support fits into a broader pattern that is reshaping American politics, as Lee Drutman argued earlier this year in Vox:

It’s important to understand that between 1990 and 2014, the share of foreign-born citizens in the United States went from 7.9 percent to 13.9 percent — a near doubling. The last time the share of foreign-born citizens got this high (about 100 years ago), it provoked enough nativist backlash in the 1920s to largely close the borders for four decades, until 1965.



… In an exhaustive 2010 study, political scientist Dan Hopkins demonstrated why some places became much more anti-immigrant than others. “A sudden increase in the number of immigrants,” he concluded, “is the most powerful predictor of which localities consider anti-immigrant ordinances.”



In a review essay on the immigration literature in political science, Hopkins and co-author Jens Hainmueller conclude, “Immigration is thus an issue with the potential to emerge suddenly and to destabilize existing political alignments.” Moreover, increases in the foreign-born share of the state population appear to help Republicans. The greater the increase the foreign-born share of the population between 1990 and 2014, the more Republicans improved their two-party vote share for president between 1992 and 2012.

The rural Midwest’s growing affinity for Trump — and the Republican Party more broadly — appears to be driven by a backlash to mass immigration. One can characterize this backlash in terms of racism and xenophobia. Or one can more generously note that NIMBYism is a nearly universal creed, and that human beings tend to resist drastic changes in the culture of the places they call home. (It seems to me there’s truth to both of these characterizations.)

Regardless, that backlash is a potent political force. And Donald Trump is unlikely to be the last right-wing demagogue to try and exploit it for contemptible ends.

Progressives must hope that the salience of anti-immigration backlash is overwhelmed by a return to robust economic growth, a slowdown in illegal immigration, or simply the progression of time — before it propels a reactionary populist to the Oval Office.