Lincoln County, Mo., a fast-growing exurb northwest of St. Louis, is one of a handful of U.S. counties that always vote for the winning candidate in presidential elections. This perfect record goes back more than a half-century. And it explains why I recently set out for that oracle county, traveling across the middle of bellwether Missouri to ask how the ultimate swing voters the white working class are looking at this year's decision.
I followed a cord of suburban and rural communities that connects the urban Democratic strongholds of Kansas City and St. Louis. After stops...