For weeks, the Republican Party and its conservative allies have drifted closer to an embrace of “replacement theory” — i.e. the idea that immigrants and particularly undocumented ones are “replacing” natural-born Americans. The claim is that they harm the country by diluting both our culture and the voting strength of the existing population.

Fox News’s Tucker Carlson has spearheaded the campaign, and a handful of GOP lawmakers and pundits have embraced it. Some even pursued a caucus aimed at upholding the country’s “Anglo-Saxon political traditions” and warning of the societal and political harms of mass immigration.

Much of the coverage has focused on how nativist and offensive that is — how closely it hues to white nationalists’ claims about “replacement.” But the other issue is how true it is and what the actual impact is.

We’ve received two key data points on this over the past week-plus, both of which provide some important context.

One came last week, from the Department of Homeland Security, which issued a report on the estimated undocumented immigrant population in the United States. The report pegged the number in 2018 at 11.4 million — lower than most years in this century, but with the numbers staying relatively flat for the past decade-plus.

The other was the Census Bureau’s announcement Monday that the United States’ population grew at the slowest pace since the 1930s — just 7.4 percent over the past decade.

We’ll tackle that one first. To be clear, the “replacement” claim is more about the percentage of immigrants in the broader population rather than the size of the overall population. But Carlson has also pushed that latter idea, which is of a piece.

“Over the past 30 years, the population of the United States has exploded by nearly 100 million people, mostly due to immigration,” Carlson said last month, adding: “This is becoming a crowded country, and crowded countries are ugly, unhappy countries. Why are we letting that happen?”

This, of course, ignored that U.S. population density is significantly lower than most of Europe and other first-world countries. But even if you grant that Carlson was talking about urban areas (or something like that) the “explosion” of the population just isn’t borne out by the numbers. During the past 30 years, population growth has actually been slower than it was for most of the 20th century. “100 million” might sound like a scary number to some, but as a percentage, this “explosion” has been rather unremarkable. In fact, we’re getting “crowded” at a slower rate than basically any point in the past century.

The other issue here is the need for population growth. Generally speaking, a population not replenishing itself is seen as a bad thing. When birthrates fall below “replacement level” — there’s that word again — it’s seen as a cause for concern because young people won’t be there to pick up the slack as the rest of the population ages out of the workforce. And women in the United States were having babies at a record-low rate in 2018. Given that, here’s certainly a valid argument to be made that we need immigrants to replenish that younger population (to whatever extent that might be).

Now to the undocumented population data. Again, we need to specify that much of the “replacement theory” rhetoric deals more broadly with immigration, rather than just the illegal type. On that, there’s at least an increase. According to data from the Census Bureau’s American Community Survey, the foreign-born population grew from 12.9 percent of the country in 2010 to 13.7 percent in 2019 (we’re still waiting for the 2020 Census’s population breakdowns). The percentage of foreign-born residents who are naturalized citizens (and can thus vote) is also increasing, bringing the percentage of Americans who are foreign-born citizens from 5.6 percent in 2010 to 7.1 percent today. One in 14 Americans isn’t exactly an overhaul of our electorate, but at least it’s actually increasing.

But much of the rhetoric often focuses on the scary prospect not of admitting immigrants legally, but allowing a flood of them illegally and then having Democrats grant them citizenship.

“So if you open the borders and then sponsor legislation giving citizenship and voting rights to the people you’ve just admitted illegally, what are you doing?” Carlson asked rhetorically last month. “You’re trying to change election outcomes, and that’s what [Democrats] are doing.”

Former House speaker Newt Gingrich (R) added on the same channel: “What if your goal was to have the maximum number of illegal people in the United States?” Fox host Steve Doocy responded: “Perhaps that’s why they’re not calling it a crisis: Because it’s working exactly as that is planned.”

Again, perhaps if we’re being charitable, they’re talking about something that might happen soon or be borne out in future data. But this was also something Republicans repeatedly floated with Barack Obama, even as the undocumented population was staying steady throughout his presidency and he deported more people than any previous president.

It also remains true the data we do have shows the percentage of the population that is undocumented is actually generally decreasing because it’s failing to increase alongside modest growth in the rest of the population.

Crucially, the number of undocumented immigrants who have stayed in the country has sharply declined when it comes to those crossing the border over the past decade, according to DHS data. In other words: We’ve been deporting many more of them as they come.

The question is why this idea is suddenly more en vogue with portions of the right without that data to back it up — and even as the data suggests there isn’t anything amounting to an “exploding” population or an increase in the undocumented immigrant population. The answer seems to be that it has a receptive audience and scaring people is good for ratings.

The struggle for the GOP is in what to do about this growing chorus. While much of the rhetoric focuses on immigrants from Latin America, the number of immigrants who become naturalized voters is actually about equal between that region and Asia. The latter are voters the GOP was once able to appeal to — even winning them as recently as the 1990s, though they have trended Democratic, particularly during the past decade. Former president Donald Trump and his allies also made a big show of his relatively strong showing among Latinos, particularly in Florida and Texas. There’s certainly a tension here between demonizing immigrants who have a growing-but-still-small influence on elections and appealing to them.

To some extent, the immigrant vote will remain a growing fixture in our politics; it grew even when Trump was in office, after all. Republicans need to ask themselves how much they want to entertain these kinds of theories about “replacement” vs. how much they want to actually appeal to these voters. The easy thing is to appeal to nativism, given that much of the party’s base seems to like that, but that doesn’t make it the smart thing.