"White nationalist, white supremacist, Western civilization—how did that language become offensive?" Mr. King said. "Why did I sit in classes teaching me about the merits of our history and our civilization?"
In the recent past (2017) King insisted that "we can't restore our civilization with somebody else's babies," and only a few years before that (2013) he insisted that "there isn't anyone that can fairly characterize me as anti-immigrant." Which pretty much tells you what kind of bubble the guy is living in: He's openly hostile to immigration, both legal and illegal, but refuses to admit as much.
Still, even if the Vietnam draft-dodger can't be swayed, it's worth at least pointing out to those who might be open to discussion that equating America with whiteness is fundamentally un-American. The United States has a deeply troubled history with race and racism, but one of the few things that makes our country different is that we aspire to be a nation that aspires (and often achieves) a sense of identity that goes far beyond blood and soil. Take it away, Jean de Crevecouer in Letters from an American Farmer (1782):
What then is the American, this new man? He is either an European, or the descendant of an European, hence that strange mixture of blood, which you will find in no other country. I could point out to you a family whose grandfather was an Englishman, whose wife was Dutch, whose son married a French woman, and whose present four sons have now four wives of different nations. He is an American, who leaving behind him all his ancient prejudices and manners, receives new ones from the new mode of life he has embraced, the new government he obeys, and the new rank he holds.
He becomes an American by being received in the broad lap of our great Alma Mater. Here individuals of all nations are melted into a new race of men, whose labours and posterity will one day cause great changes in the world.
I've noted elsewhere that Crevecoeur has his limits (among other things, he speaks only of men and he owned slaves for a time). But he accurately captures a process by which America is a country that has long aspired to be a place where people could be judged, in Martin Luther King's phrase, by the content of their character rather than the color of their skin.
It's disturbing that members of the federal government, such as Steve King, persist in identitarian politics. Yet in a country that is more genuinely diverse and less racist than ever, his sort of thinking signals nothing more than the death rattle of the racial collectivism that has always stained American history.