The trick lies in not seeing the trick

To form a government, Sánchez either needs a parliamentary majority – which seems impossible – or at least a majority of ‘yeses’ over the ‘nos’ with the doubtful parties relying on abstaining.  Unfortunately, the three right-wing parties of PP, Vox and Ciudadanos won’t allow this situation to ease by abstaining, leaving us with the current scenario. So far, the plan to join with Unidas Podemos has received the support of 92% of PSOE militants who answered the consultation (here). Currently, attention is focused on gaining the tacit support of the ERC, the Esquerra Republicana de Catalunya (wiki). 

The ERC is an independence party with its leader Oriol Junqueras imprisoned for thirteen years for ‘sedition’. The party has consulted its militants and found 95% won’t support an arrangement with the PSOE without ‘a negotiation over Catalonia’. (Or, as El País gamely puts it: ‘Massive support of the ERC militancy to the leadership plan to negotiate the investiture of Sánchez’). That arrangement says Moncloa.es here, would include pardoning the political prisoners jailed (or in exile) over the pròces.

‘Critics of the PSOE warn: the pact with Podemos and ERC "puts coexistence at risk"’, says VozPópuli here, adding ‘A debate platform called La España que reúne, sponsored by the former French socialist minister Manuel Valls, warns that "Spain is in a troublesome situation" and that a PSOE and Podemos government pact, with the inevitable support of an ERC that has not renounced its plan to break the unity of the country "would be a very serious political error and irresponsibility that would put our freedoms and citizen coexistence at risk"...’. The platform would like to see a PSOE-PP-C’s partnership. José María Aznar is also fully against a PSOE/Podemos government and says ‘you’ll be hearing a lot from me in the future’ (here).

If all goes to pot, then a fresh election will be held, says El Español, on April 5th 2020.