Legislation to curb gun violence won’t happen until Americans mobilize to demand it, U.S. Sen. Cory Booker said Sunday. Booker, who helped join a Senate filibuster in 2016 to force a vote on gun safety legislation following the mass murder of 49 people at a gay nightclub in Orlando, Florida, said supporters of stronger regulations need to pressure Congress to act. “As Frederick Douglass said, ‘Power concedes nothing without a demand,’” Booker said on NBC’s “Meet the Press.”. “If there’s no struggle, there is no progress. We have got to begin to hold our congressional leaders more accountable f…