On Oct. 11, 2016, Michael Foster and two companions rose before dawn, left their budget hotel in Grand Forks, N.D., and drove a white rental sedan toward the Canadian border, diligently minding the speed limit. As the driver, Sam Jessup, and a documentary filmmaker, Deia Schlosberg, recorded events from the back seat. For months, he’d imagined his next actions: He would snip the padlock that secured the gate and approach the blunt length of vertical pipe in the center of the enclosure — the stem of a shut-off valve for the 2,700-mile-long Keystone Pipeline. What neither the sheriff’s department nor...