Federal authorities made their first arrest Thursday in connection with two pipe bombs that were planted outside the Democratic National Committee and Republican National Committee headquarters on the eve of the Capitol riot on Jan. 6, 2021, according to two sources familiar with the matter. The arrest marks a major step forward in a case that has vexed the FBI for nearly five years. Both pipe bombs were placed outside DNC and RNC headquarters on the evening of Jan. 5, 2021, federal investigators have said. The devices — made out of 1x8-inch pipes, kitchen timers and homemade black powder —...