 In 2015, Castro departed from the PRD and ran as the Morena candidate in the Baja California Sur gubernatorial election of that year, finishing fourth with 6.41 percent of the vote as the state reaffirmed its shift to PAN dominance by re-electing that party in the person of Carlos Mendoza Davis.In December 2017, Castro announced his intention to seek the Morena nomination for Senate in 2018.On election day, the Juntos Haremos Historia ticket of Castro and Lucía Trasviña Waldenrath placed first, sending both candidates to the Senate.