Ever since he came down that golden elevator in Trump Tower in 2015, President Trump has been waging a culture war that has gradually become more provocative, racialized and nativist. The culmination, to this point, came this weekend when Trump urged nonwhite Democratic congresswomen to go back to their countries (even though only one of the women is actually an immigrant and all are U.S. citizens).

Trump’s tweets effectively mimicked a controversial segment Fox News host Tucker Carlson did on Rep. Ilhan Omar (D-Minn.) last week. And indeed, Carlson seems to be increasingly serving as Trump’s spirit animal, dishing up a steaming helping of anti-immigrant rhetoric nightly on his show — as well as increasingly decrying the concept of diversity.

To see Trump and Carlson operate, you’d think this kind of attitude was on the rise in American politics, or at least the Republican Party. But you’d think wrong.

If anything, Trump’s presidency has accompanied an increasing belief in the contributions of immigrants and the importance of diversity, polls show. And to whatever extent Trump and Carlson have seized upon nativism and anti-immigrant sentiment in the Republican Party, it seems to have been of the sort that already existed.

HuffPost and pollster YouGov have asked Americans in recent years whether immigrants threaten American values or strengthen our society. In June 2016, Americans said 48-to-34 percent that they were more of a threat; in December 2018, Americans said they 41-to-36 percent that they, by and large, strengthened the country.

The same poll shows the receptivity among Republicans to this kind of message. But even there, it’s on the wane. While 75 percent of Republicans in 2016 said immigrants threatened American customs and values, that number dropped to 67 percent in late 2018.

An NBC/Wall Street Journal poll has shown a similar shift. In July 2015, when Trump got into the 2016 race, Americans were about evenly split on whether immigrants helped (47 percent) or hurt (43 percent) the country more. By September 2018, the gap was 2-to-1 — 61 percent and 28 percent — toward immigrants helping more than they hurt.

There was little change among Republicans, but it didn’t suggest opposition to immigration is ascendant there, either. While in 2015, Republicans said 54 to 35 that immigrants hurt more than they helped, in 2018, the margin was 48 to 39.

A third poll, from the Pew Research Center, reinforces the trend. Asked whether immigrants are a “burden” or they “strengthen” the country, the shift has been steady over the last quarter century. And even among Republicans and Republican-leaning voters, the numbers have been static since Trump came on the political scene.

The poll numbers don’t directly capture what Trump was tweeting about this weekend, but they instead deal more with generalized feelings toward immigrants — both legal and undocumented. But Trump’s comments about our immigration system have run the gamut, from decrying the scourge of illegal immigration to targeting legal immigrants, including those seeking asylum, those from what Trump called “shithole” countries and now members of Congress who aren’t immigrants but who Trump apparently thinks should leave the country anyway.

The uniting theme — and it’s one reinforced nightly on Carlson’s program — is that immigrants are to be dealt with suspiciously and that ones who don’t speak about this country glowingly enough actually “hate” this country. Whatever you think about what our immigration laws should be, it’s clear Trump would like to pit his supporters and Americans more broadly against immigrants who don’t check the right boxes.

There’s no telling how this will play out in 2020 — and Democrats’ leftward moves on illegal immigration could certainly play a role — but the evidence suggests support for this kind of rhetoric in American society has an expiration date.

Scott Clement contributed to this report.