The annual U.S. death toll from illegal drugs, which has risen nearly every year since the turn of the century, is expected to fall substantially this year. The timing of that turnaround poses a problem for politicians who aim to prevent substance abuse by disrupting the drug supply. Those politicians include Republican presidential nominee Donald Trump, who promises to deploy the military against drug traffickers, and his Democratic opponent, Vice President Kamala Harris, whose platform is also heavy on supply-side tactics. Neither candidate seems to have absorbed the lessons of the “opioid e…