FRANKENSTEIN, Germany — They called it the Frankenstein coalition, and not just for the location.

When the Frankenstein chapter of Chancellor Angela Merkel’s conservative party defied Berlin and formed an alliance with the far right in the village council, some considered it monstrous.

To many, the alliance violated one of the biggest taboos in German politics: that no mainstream party collaborate with the far right.

“A red line was crossed,” said Eckhard Vogel, the mayor of Frankenstein, a centrist who belongs to neither party. “You can’t go to bed with people like that.”

In Frankenstein, a small village in southwestern Germany, Ms. Merkel’s Christian Democrats and the Alternative for Germany do in fact share a bed, literally: They are husband and wife.