For more than two decades, much of Southern Arizona was represented by Rep. Raúl M. Grijalva, a liberal stalwart who championed environmental causes, supported immigrant rights and advocated on behalf of indigenous communities.

Arizona Democrats on Tuesday will choose their nominee to run for a vacant U.S. House seat in September, as the party grapples with demands for generational change and divisions over just how progressive it can be in the era of President Donald Trump.