But it’s not just a personal matter. Ms. Merkel governs in partnership with the left-wing Social Democrats, who support marriage equality, but in populous Bavaria the conservative wing of the coalition is represented by the C.D.U.’s sister party, the Christian Social Union, which strongly celebrates its closeness to the Roman Catholic faith, the church and its religious customs. At the same time, the party is drifting ever further to the right, embracing openly xenophobic, anti-refugee ideas (to such an extent that the Catholic bishops of Bavaria and the archbishop of Cologne, among the most powerful clergymen in the country, found themselves compelled to reprimand the C.S.U. for its un-Christian conduct).

The C.D.U. is also looking to reinforce its conservative image. In recent years the party has capitulated on several key issues, which until then were considered to lie at the core of their policy: compulsory military service and nuclear energy, to name just two prominent examples. There aren’t many such issues left, but marriage equality is one of them. For many in the party, giving in on gay rights would be the equivalent of selling the silverware. Several C.D.U. members have defected to the upstart, far-right Alternative for Germany Party, which upholds the biblical family model and rejects marriage for all.

With the Social Democrats stuck at around 20 percent nationwide, and despite Ms. Merkel’s own ups and downs in the polls and recent losses by the C.D.U. in elections in eastern Germany, her party is on track to win the national elections convincingly next fall. (Of course, if she decides not to run again for the top spot, and a younger, more progressive candidate steps in, the chances for marriage equality could change.)

A result, at least for now, is an odd reversal of Western Europe’s league tables for social progress. Traditionally, it is the Protestant countries of the north that have led on progressive social issues, with the Catholic south dragging behind. This time, though, it is Germany, the leading country in Protestant Europe, that lags the rest. Without a major realignment in German politics, that is unlikely to change for a long time to come.