Europeans tend to talk about “ultra-nationalism” or “xenophobia” or “racism” rather than nativism, said Mudde, who is Dutch. But this language, in his view, doesn’t fully capture the phenomenon, which “isn’t just a prejudice [against] non-natives” but also “a view on how a state should be structured.”

Nativism, Mudde told me, is “xenophobic nationalism.” It is “an ideology that wants congruence of state and nation—the political and the cultural unit. It wants one state for every nation and one nation for every state. It perceives all non-natives … as threatening. But the non-native is not only people. It can also be ideas.” Nativism is most appealing during periods when people feel the harmony between state and nation is disappearing.

Eric Kaufmann, a political scientist at the University of London’s Birkbeck College, calls nativism a “crude” term and prefers something more precise: “majority-ethnic nationalism,” which applies to people who consider themselves native to or settlers of a country and want to protect their “demographic predominance in that territory.”

Some types of nationalism are concerned with ideology (America as the leader of the free world) or status (American as the most powerful country in the world). But ethnic nationalism is “less concerned with getting to the moon and being number one,” Kaufmann said. It’s a “boundary-based nationalism.”

Nativists typically spend more time defining “them” (non-natives) than “us” (natives), Mudde added, because the more specific the “us,” the more it raises thorny questions of national identity and excludes segments of the population who might otherwise support the nativist politician. The native is often depicted as the unspoken inverse of The Other: “The other is barbarian, which makes you modern. The other is lazy, which makes you hardworking. The other is Godless, which makes you God-fearing.”

Long before Trump embraced the slogan “America First,” Elisabeth Ivarsflaten taught her students at the University of Bergen in Norway to think of nativist politicians as the “my-country-first party.” All political leaders should (theoretically) put their country’s interests first. But nativism goes beyond that logic. “The idea that these parties roughly engage is that too much emphasis is being put on internationalization and accommodating people who want to come into the country” but aren’t originally from there, Ivarsflaten said. Whether nativism involves opposing the European Union because Germans have to bail out Greeks, or opposing multiculturalism because it means accepting forms of Islamic dress, the idea is that “there is a native population or a native culture that should be given priority over other kinds of cultures.”

Ivarsflaten places nativism in the broader category of right-wing populism, an ideology premised on representing the virtuous “people” against a corrupt “elite.” She has found that all the populist-right parties that performed well in Western European elections in the early 2000s had one thing in common: They tapped into people’s complaints about immigration. Other grievances—regarding the European Union, economic policy and the state of the economy, or political elitism and corruption—did not account for the success of these parties as consistently or powerfully as immigration issues did. “As immigration policy preferences become more restrictive, the probability of voting for the populist right increases dramatically,” she wrote at the time.