FILE - A demonstrator kneels and uses a makeshift shield as federal agents launch tear gas during a Black Lives Matter protest at the Mark O. Hatfield United States Courthouse in Portland, Ore., on July 29, 2020. Questions posed by lawmakers, medical workers and experts about the safety of tear gas remain unanswered, even after more than a dozen U.S. senators asked a congressional watchdog to look into the issue. (AP Photo/Marcio Jose Sanchez, File)