WASHINGTON (AP) — With frustration mounting, President Barack Obama sought Thursday to quell doubts he’ll use his presidential powers to act on immigration, telling Hispanics and immigration activists it’s “not a question of if but when.”

At the Congressional Hispanic Caucus Institute’s annual gala, Obama warned activists that his eventual actions will spark intense political opposition that could threaten the durability of what he does. In a partisan pitch a month before Election Day, he urged Hispanics across the U.S. to use their votes to improve prospects in the future for a legislative fix.