Milwaukee’s 1956 pounds out the heavy, chugging alternative-rock riffs like the ones that proliferated throughout the early ’90s, but underneath the grind, the band reveals an unexpected softer side. “Persistent,” one of the standout tracks from the group’s measured 2007 album, Saboteur, is steeped in the same bleary-eyed pensiveness that made The National’s Boxer such a treat. 1956 tops a 10 p.m. bill at the Cactus Club tonight.