In a national vote widely viewed as a victory for conservatives, last year’s elections also yielded a win for liberals in eight states that legalized marijuana for medical or recreational use. But the growing industry is facing a federal crackdown under Attorney General Jeff Sessions, who has compared cannabis to heroin.

A task force Mr. Sessions appointed to, in part, review links between violent crimes and marijuana is scheduled to release its findings by the end of the month. But he has already asked Senate leaders to roll back rules that block the Justice Department from bypassing state laws to enforce a federal ban on medical marijuana.

States Keep Saying Yes to Marijuana Use. Now Comes the Federal No.