WASHINGTON (AP) — Even as a series of states legalized the recreational use of marijuana, the possession, use or sale of the drug remained a federal crime. Still, the Justice Department, under President Barack Obama, took a hands-off approach.

That changed Thursday. Attorney General Jeff Sessions revoked an Obama-era policy that was deferential to states' permissive marijuana laws. Sessions is leaving it up to federal prosecutors in states that allow drug sales and use to decide whether to crack down on the marijuana trade.

The move by Sessions has generated outrage among advocates for legal m...