MILLCREEK, Utah — Ben McAdams, a candidate for Congress, was speed-walking along the highway shoulder in his business suit, safety and common sense be damned.

“We’ll make it,” he said, as the trucks whistled by, blowing dust into the Utah sun.

In his bid to unseat Representative Mia Love, a Republican, Mr. McAdams has been trying to do just that — make it, in this case to the United States House as a Democrat from a state that runs about as red as the desert is dry. The district he seeks to represent, Utah’s Fourth, is a boot-shaped expanse extending south from Salt Lake City where fewer than 15 percent of the voters are registered Democrats.

In any other year, a McAdams win would seem improbable.

Ms. Love, the only black Republican woman in Congress, won her last election by nearly 13 points, and many voters see her as an outgoing leader in a place where women — especially conservative women — are rarities in the halls of power. She is the sole Republican member of the Congressional Black Caucus, making her an uncommon symbol of bipartisanship in an era of deep division.

But this is Utah, where Mormon values dominate political choices and voters largely rejected Donald Trump, whose crass commentary and hard line on immigration clash with church doctrine, garnering him just 45 percent of the vote in 2016.