Immediately after the horror of the Feb. 14 mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, the National Rifle Association halted all of its digital advertising, including ads on YouTube, banner ads on websites, and Facebook ads. Within four days, though, the NRA had returned in force, increasing its advertising aggressively on Facebook, and spending so widely and indiscriminately that its ads on YouTube showed up on videos for school-age kids.