As winner of the most seats in April's general election, and having been officially appointed last week as candidate to be prime minister by the king, Pedro Sánchez is searching for support from other parties to reach a majority of MPs.
Negotiators from his PSOE party have been meeting with possible partners either to form a coalition or merely to agree their abstention to allow in a minority Socialist government.
On Wednesday, the party's number three and head negotiator, José Luis Ábalos, said that he wasn't ruling out a "government of cooperation" between the PSOE and Unidos Podemos, which would see the more left-wing party getting some ministerial posts. He also opened the door to a form of deal with the MPs of the Catalan separatist parties which had been rejected up to then.
Ábalos met with leaders of smaller parties on Wednesday, including Basque nationalist PNV. He blamed the Partido Popular and Ciudadanos, the main opposition parties, for needing to talk to Unidos Podemos and separatists as they will not be abstaining in July's investiture vote in Congreso.