Over the decades, Republican domination has overtaken politically competitive counties

As recently as 1996, two-thirds of the roughly 3,000 U.S. counties had highly competitive U.S. presidential elections. The remainder were about evenly split between strong Democratic support and strong Republican support. But in the years since, the number of counties that are reliably Republican has nearly tripled, the number of reliably Democratic counties has been cut in half, and only about one-fourth of all U.S. counties are competitive between the parties.