Three years later, the PPS nominated the aforementioned Gascón Mercado as its candidate for the governorship of Nayarit in the 1975 state election.

[4] Gascón Mercado and the local membership of the PPS protested the results, accusing the PRI of electoral fraud and demanded that the election be nullified.

The party broke with the PRI at the federal level for the first time in the 1988 presidential election, choosing instead to support the candidacy of Cuauhtémoc Cárdenas and entering his National Democratic Front.

[7] This result (second to last among nine presidential candidates) implied the loss of the official registry to her party, which was recovered in 1997, and then lost again definitely after the midterm elections of that year.

The PPS's traditional political space (i.e. to the left of the PRI) was largely captured by the Party of the Democratic Revolution (PRD) since 1989.