Spain’s acting prime minister, the socialist leader Pedro Sánchez, has been invited to try to form a government two months after July’s inconclusive snap general election, and four days after the leader of the conservative People’s party (PP) failed in his bid to take office. King Felipe on Tuesday formally nominated Sánchez to attempt to secure congress’s backing to form a new coalition administration with the leftwing Sumar alliance. Although the PP narrowly defeated the socialists in July, it failed to secure a parliamentary majority and its leader, Alberto Núñez Feijóo, was unable to attract the support he needed to become prime minister in last week’s investiture debate. The nomination means Sánchez has until 27 November to put his candidacy before MPs in another investiture debate and vote. If he proves unsuccessful, parliament will be dissolved and Spain will return to the polls in mid-January for its sixth general election in nine years. Sánchez’s biggest challenge will be navigating the controversial and complicated issue of the amnesty that Catalan pro-independence parties are demanding in return for lending him their votes. Last month, the self-exiled former Catalan president Carles Puigdemont – who leads the hardline separatist party Junts – said support for Sánchez would be conditional on the dropping of all judicial cases against himself and hundreds of others over their roles in the failed unilateral bid for regional independence in October 2017. Feijóo has repeatedly attacked Sánchez over the possible amnesty, arguing that agreeing to the demand would be cowardly and cynical, and would serve as further proof of his opponent’s desire to remain in power whatever the cost. Nine days ago, more than 40,000 people joined a rally in Madrid to protest against the mooted measure. The acting prime minister has so far deliberately avoided explicit mention of an amnesty. He again chose his words carefully as he addressed a press conference on Tuesday afternoon, recalling that he had inherited a divided and turbulent Catalonia from the previous PP government when he took office in 2018. “I think the situation in Catalonia today bears no resemblance to the one I found when I had the honour of becoming prime minister,” he said. “I’m going to carry on down that path, which is the path of politics. And doing politics necessarily involves generosity, being committed to your country – and leadership.” Sánchez added: “Whatever we do will be within the constitution and whatever we do will be to serve the common interest … and the coexistence and harmony between Spaniards.” He also defended the decision he took two years ago to grant pardons to nine Catalan independence leaders for their parts in the push for secession. “When I decided to issue the pardons, I trusted in the beneficial effects they would have when it came to coexistence in Catalonia and to getting over what happened in 2017,” he said. “I trusted in that back then, but I can now confirm that that decision was the right one and that I was right to take it in the general interest.” Feijóo greeted confirmation of Sánchez’s candidacy by saying Spaniards could expect “weeks of lies” as the socialist leader tried to enlist the support necessary to return him to the Moncloa Palace. “[There will be] dark negotiations because the talk will be more about seats than about the problems people face,” he said. “There will be more talk of deals than of the reforms families need, and no democratic principle nor institution will find itself above being traded.”