As a candidate for Popular Action, Sandro was elected deputy for Lima in 1962, performing his legislative function from 1963 to 1968.
After the coup d'état of October 3, 1968, perpetrated by General Juan Velasco Alvarado, he suffered persecution, like the rest of the leading men of the Belaundista government.
After the announced return to democracy, he ran for Senate of the Republic in the general elections of 1980, in which his party led by Belaúnde again triumphed.
He had to face the problem of rampant inflation and the economic crisis, as well as the terrorist actions of the Shining Path.
He supported his party's participation in the FREDEMO electoral alliance, which nominated writer Mario Vargas Llosa for president.