That is not least to avoid confusion with the other Trumps (or “Droomps,” as the name is pronounced in Palatinate dialect) listed in a phone book for the area: Beate Trump, a podiatrist in another nearby village, for example, or Justin Trump, a teenager whose friends say he sometimes gets teased for orange-blond hair.

But the Weisenborns and the Geissels and the Benders and the Freunds in Kallstadt are related to Mr. Trump, too. “Practically half the village is,” chuckled Kallstadt’s mayor, Thomas Jaworek, before quickly adding: “I’m not.”

Both of Mr. Trump’s paternal grandparents, Friedrich and Elisabeth Trump, were born in Kallstadt, home now to 1,200 inhabitants. Growing up directly opposite each other, they were baptized in the village church and married a few miles down the road before emigrating to the United Stat