Senator Cory Gardner, Republican of Colorado, where legalized marijuana has spawned a $1 billion industry, threatened to block all nominees to the Justice Department until the new policy is dropped.

Representative Dana Rohrabacher, a California Republican, laid the blame at the feet of Mr. Sessions, saying he “betrayed us on this.” A 2014 law co-sponsored by Mr. Rohrabacher prohibits the Justice Department from going after users, growers or sellers of medical marijuana in states where it is legal. The use of recreational marijuana became legal in California on Jan. 1. Even Matt Gaetz, the Florida representative last seen trying to get the special counsel Robert Mueller fired, said the new policy showed Mr. Sessions’s “desire to pursue an antiquated, disproven dogma instead of the will of the American people.”

None of this will bother the attorney general, a lifelong antidrug crusader who runs the Justice Department like it’s 1988, when the war on drugs was at full throttle and the kneejerk political response was to be as punitive as possible. Mr. Sessions has long held a particular enmity for pot, which he continues to demonize. “Good people don’t smoke marijuana,” he said in 2016.

This is wrongheaded for so many reasons. It’s out of step with current knowledge about the risks and benefits of marijuana, which the federal government classified as a Schedule I drug in 1970. By that definition, it has no accepted medical use and is more dangerous than cocaine. Obviously this is outdated, and Congress needs to do its part by removing marijuana from Schedule I. But nothing is stopping Mr. Sessions in the meantime from accepting scientific facts.

The new policy is also blind to the massive cultural shift toward legalization that has been happening at the state level in recent years, after decades of outrageously harsh punishments that have fallen disproportionately on the shoulders of people of color. Eight states have now legalized marijuana for recreational use. California is now the world’s largest legal market for pot. Twenty-nine states and the District of Columbia allow marijuana to be used for medical purposes. By the end of this year, it is estimated that legal marijuana will be a $9 billion industry.