A federal jury on Friday convicted pro-Trump troll Douglass Mackey of plotting to trick voters out of casting a ballot during the 2016 presidential election. The case, which sought to address if any of the toxic stew of Internet disinformation during the 2016 election rose to the level of a crime, has been closely watched by both anti-extremist groups and right-wing politicians and pundits. Mackey, 33, of West Palm Beach, Fla., who gained fame on the Internet as the Twitter user “Ricky Vaughn,” posted two images made to look like fake Hillary Clinton ads telling people they could vote by...