Mr. Sánchez wants to give greater recognition to the victims of Franco, in accordance with a law of historical memory. That measure was approved in 2007, under a previous Socialist government, but was shelved and deprived of government funding under a conservative government led by Mariano Rajoy. One of the main goals of the 2007 law was to facilitate the opening of over 2,000 mass graves to identify the remains of those inside, most of whom died during the civil war.

For now, Mr. Sánchez has made it a priority to remove Franco’s remains from the basilica of the Valley of the Fallen, which the general had built to honor those who “fell for God and Spain” in the civil war. But the plan has been stalled by a legal dispute with Franco’s relatives, who argue he can be reburied only in Madrid’s cathedral. Politicians are also feuding over what to do with Franco’s current burial site once his remains are moved.

For Mr. Moreno, Franco not only needs to be physically removed from the Valley of the Fallen but also reinterpreted in Spanish history books, so as to get “the same treatment as Hitler and Mussolini, the other fascist war criminals.”