Last summer, as one city after another broke out in protest against the murder of George Floyd, some of the most enduring images were not of the demonstrators, but of the police: decked out in riot gear, aiming automatic weapons at peaceful crowds, and riding around on armored vehicles built for war. The crackdowns on protesters renewed furious demands to end a suite of federal programs that have put billions of dollars’ worth of military weapons in the hands of local police.