Rebellious Democrats shut down the House’s legislative work on Wednesday, staging a sit-in on the House floor and refusing to leave until they secured a vote on gun control measures before lawmakers’ weeklong break. Exasperated Republicans were forced to recess while cutting off cameras that showed the protest. But in an unprecedented step, C-SPAN used live video feeds from one lawmaker’s Periscope account and another’s Facebook page to transmit words and images from the House. Nearly 100 Democrats led by Georgia Rep. John Lewis demanded a vote on measures to expand background checks and block gun purchases by some suspected...