How white nationalists aligned themselves with the antiabortion movement

Last fall, speaking to a far-right Austrian magazine, the Iowa Republican congressman Steve King succinctly laid out his theory of Western decline. The problem, he suggested, was a demographic born at the nexus of reproduction and immigration. “If we continue to abort our babies and import a replacement for them in the form of young violent men, we are supplanting our culture, our civilization,” King said.

King had already called attention to himself the previous year for retweeting a cartoon that depicted the nativist Dutch party leader Geert Wilders as...