In the waning years of Franco's rule, from 4 March 1971 to 24 April 1974, the dictator gave Santiago a task as political as it was military: serve as governor-general of Spanish Sahara after Spanish forces had massacred members of a native independence movement in the "Zemla Intifada".

[1] Under the administration of Adolfo Suárez, Santiago remained the principal deputy prime minister but gave up oversight of the defense ministry.

[1] While Arias Navarro had been considered a Francoist, Suárez would turn out to be a reformer, putting Spain on the road to democracy.

Out of office, Santiago continued to meet with conservative military officials disturbed by Spain's democratization and liberalization.

In September 1977, he met with a group of army leaders—including Jaime Milans del Bosch—who secretly wrote a letter to King Juan Carlos I asking him to undertake "actions to rescue the destiny of the Fatherland".