If you paid close attention to what Mr. King was saying those 16 years about Mexicans, you would hear the same thing he says in white supremacist soirees. But now it is making waves. People are getting wary. The same voters who used to think he was a straight shooter speaking his mind got uncomfortable seeing poor children locked up in cages at the border. In January, the Des Moines Register’s Iowa Poll, conducted by the reputable Selzer and Co., found that 69 percent of Fourth District voters actually support a path to citizenship for undocumented immigrants.

After Mr. King visited the Austrian headquarters of the Freedom Party, founded by a Nazi SS member, Land O’ Lakes, a regional dairy cooperative, pulled its support. So did Intel. The leader of the National Republican Congressional Committee, Representative Steve Stivers of Ohio, condemned Mr. King’s support for white nationalists. “We must stand up against white supremacy and hate in all forms, and I strongly condemn this behavior,” Mr. Stivers said last week.

Mr. Scholten is picking up steam. A 38-year-old paralegal and former minor-league pitcher, he is a fifth-generation Iowan who tools around the district in a used Winnebago christened “Sioux City Sue.” He is friendly and knows how to speak Iowa shucks. The Sioux City Journal, which backed Mr. King in previous elections, announced that it had enough of the congressman’s racist blunderbuss and endorsed Mr. Scholten. The earth shook just a little next to the Missouri River.

Mr. King says he will win as he always has by firing up the base — and he might be right. Beware the caravan from Honduras, the women and children in flip-flops, he relentlessly warns. They might invade his hometown, Kiron, population 273, which certainly could use a few more souls even if they are “not of our culture.” When you have nothing to sell — tax cuts are no good when you’re losing money on that pile of corn outside — fear is always a sure standby.

If Mr. King wins, it will be because Republicans outnumber Democrats here 190,000 to 120,000, while independents number 172,000. That Mr. Scholten is even in the conversation is a wonder. Fear of immigrants might have worn out its welcome when Sioux County, 80 percent Republican, decides that Latinos are pretty good help in the dairy barns. If we run them off as Mr. King and Trump demand, then who’s going to milk those cows and scoop hog manure from a pit?

It’s harder to hate or fear someone you know, as Storm Lake learned.

Art Cullen, the editor and a co-owner of The Storm Lake Times in Iowa, won the 2017 Pulitzer Prize for editorial writing and is the author of “Storm Lake: A Chronicle of Change, Resilience, and Hope from a Heartland Newspaper.”

Follow The New York Times Opinion section on Facebook, Twitter (@NYTopinion) and Instagram.