Most polls suggest the PP would win a general election expected at the end of the year but would need the support of Vox to govern.
Before that, Spain will vote in May in regional and local elections.
Lacking a parliamentary majority, Sanchez's government has been forced since its formation to negotiate with Basque and Catalan separatists to pass bills, which has angered many on the right.
Conservatives accuse Sanchez of having eliminated the crime of sedition to assure the continued support of Catalan pro-independence party ERC in tight parliamentary votes.
But the government argues sedition is an antiquated offence that needed to be replaced with one better aligned to European norms.
