Republican Rep. Steve King of Iowa. Associated Press/Charlie Neibergall For members of a movement that purports to focus on putting American interests first, American nationalists seem to spend an awful lot of time obsessing about Europe.

Europe's birthrates are too low and Europe has Muslim minorities that it's not integrating well, Republican Rep. Steve King of Iowa complains, by way of defending his tweet that said, "We can't restore our civilization with somebody else's babies."

King's tweet was in praise of the Dutch nationalist politician Geert Wilders, who is running on a platform of caustic opposition to Muslim immigration.

Europe has specific problems related to population policy. The birthrate in the EU is 1.61 children per woman, lower than 1.87 in the United States. Europe has a significant problem with homegrown terrorism from its Muslim communities, in part because Europe's Muslim immigrants are poorer, more numerous, and less well-integrated than those in the United States.

These are real problems worthy of attention from European politicians, though I do not believe Wilders has the right approach to them. But what does any of this have to do with the United States, and why does King spend so much time thinking about it?

I think the answer is that American nationalists tend to oppose immigration for reasons that are fundamentally racist. They want white people to have more babies and fewer minorities to come here.

But the facts on the ground in the United States are not useful for arguing that case without explicit appeals to racism. So they obsess over Europe, where immigration has created more problems and birthrates are dire.

Pro-immigration politicians in the United States would do well to think about what it is about immigration to the United States that makes it work better than in Europe — and how we can adjust our immigration policies to improve those advantages.

In the case of our Muslim communities, it is important to note that Muslim immigrants to the United States tend to be disproportionately educated. Instead of a disaffected Muslim underclass suffering from high unemployment, we have prosperous and well-integrated Muslim communities. This success is in significant part a matter of how immigrants have been selected to come to the United States.

But overall, American immigration policy is a hodgepodge.

A lot of immigrants are admitted for reasons that have no clear link to the American national interest. And by allowing immigration laws to go unenforced for so long, we have allowed millions of unauthorized immigrants to choose the United States, instead of us choosing them.

There's nothing wrong with a country making immigration policy based on what kind of society it wants to build. That policy shouldn't aim at producing ethnic homogeneity. But we should be able to explain what it does aim to build.

An immigration policy based on clear, non-ethnicity-based principles — similar to the "points" systems used in Canada and Australia that favor highly skilled and English-proficient immigrants — would make it easier to win over voters who are not committed to King's thinly disguised concerns about ethnicity, but who may have a vague concern that many immigrants are not a "good fit" for the United States.