Crossposted on MSNBC

The Senate Judiciary Committee held a hearing this week to discuss an emerging tension in marijuana policy. Washington and Colorado have legalized small amounts of marijuana and 20 other states have legalized it for medical use. These policies put the federal government into something of a quandary: since marijuana is illegal for any use under federal law, should the feds enforce its laws in these states?

The federal government has devised a temporary solution that skirts the problem and could create a series of new ones.

Last month, the Department of Justice released new guidelines on marijuana prosecutions. The essential message was that federal prosecutors should not interfere with state marijuana laws. Prosecutions should be reserved for those who sell marijuana to minors, use state laws as a cover for illegal drug sales, or as a means to distribute marijuana in states where it remains illegal.

Judiciary Chairman Patrick Leahy was unambiguous about his support. “The absolute criminalization of personal marijuana use has contributed to our nation’s soaring prison population and has disproportionately affected people of color,” said the Vermont Democrat.

But soon there were questions about whether marijuana television commercials would run in Colorado, or if there was a plot to addict the nation’s kids to harder drugs through pot-laced gummy bears.

While drug legalization advocates are hailing the new guidelines as “the most heartening news to come out of Washington in a long, long time,” many are skeptical. The Judiciary Committee’s ranking Republican, Senator Charles Grassley of Iowa, condemned Colorado’s approach and the Justice Department’s new policy. He asked Deputy Attorney General James Cole, who wrote the guidelines, “Why has the Justice Department decided to trust Colorado? Colorado has become a significant exporter of marijuana.”

But there is reason even for drug reform advocates to be wary: the new approach will do little to mitigate the failed “war on drugs” and it puts the Justice Department in an untenable position.

First, the change in the Justice Department’s stance is only advisory. The directive to the nation’s U.S. Attorneys can easily be reversed by Cole’s successor. This is not an actual change to the federal drug laws. The federal government will continue to prosecute drug crimes, which trigger harsh mandatory minimum sentences. These overly punitive sentences have led to almost half the federal prison population locked up for drug convictions.

Second, because of the preemption doctrine (in which federal law displaces contradictory state law), prosecutors are opting not to enforce laws they are sworn to uphold. That may be laudable when it comes to marijuana but would not be so praiseworthy if the issue were, for example, voting rights. Grassley understood this when he said it was “disastrous” that the Justice Department was “giving the green light to states that decide to ignore laws they don’t like.”

Criminal justice reform advocates should not be diverted by this recent shift. To create genuine and lasting progress, federal drug laws must be completely revamped. Congress should remove harsh mandatory minimums for drug crimes–or remove crimes like possession of marijuana from the list of jail-able crimes. Better yet, it should commission and evaluate public health data on whether marijuana actually should be classified as a “dangerous” drug—and if it isn’t, Congress should rethink criminalizing and punishing it so harshly.

In this way, the federal government can lead the nation toward a sane criminal justice system–one that protects the public from the serious safety threats and prosecutes and incarcerates only when absolutely necessary.