In a largely unexpected development late last week, the Department of Justice announced new guidelines addressing the federal government's contentious relationship with states over marijuana policy, a conflict that dates back to the Clinton administration.

The memo to U.S. attorneys nationwide indicates the Obama administration will not preemptively challenge implementation of marijuana legalization initiatives adopted by voters in Colorado and Washington by decisive margins last year. The guidelines set out relatively sensible priorities federal prosecutors should use in assessing -- and accepting -- state-based marijuana policies, including the medical marijuana laws adopted by 20 states so far.

This announcement comes on the heels of Attorney General Eric Holder's recent policy statement on the malignant impact of mandatory minimum sentences on this country's highest-in-the-world incarceration rates.

Some observers last week were quick to point out the Obama administration's tortured history on the conflict with state pot laws underscored by record-setting raids on medical marijuana dispensaries. Moreover, these are only guidelines; federal prosecutors still have enormous discretion in what cases they charge. Crucial banking and tax laws, let alone the underlying ban on marijuana, are also unchanged. And finally, the next administration could even potentially undo these reforms.

Yet it's not difficult to interpret the DOJ memo as a good faith attempt to move the country beyond the federalism quagmire that has consumed U.S. marijuana policy since 1996 when California defied the ban by adopting the country's first medical marijuana law.

The memo essentially restates the position the administration originally proposed in 2009, but it goes one crucial step farther. First it posits that limited federal enforcement resources shouldn't focus on entities that comply with "strong and effective" state marijuana regulations. But the new document leapfrogs that notion by suggesting these state-based systems could actually benefit federal interests.

It proposes that "robust" regulation of medical or even recreational marijuana "may affirmatively address [federal drug control] priorities by ... prohibiting access to minors, and replacing an illicit marijuana trade that funds criminal enterprises with a tightly regulated market."

That language might as well have been copied from a marijuana legalization web site. Banning outright a substance that is already so widely available and consumed only fuels an enormous underground economy, guarantees profits to criminal syndicates and won't diminish underage access the way licensing, education and age restrictions do.

Echoing arguments marijuana reformers have made for decades, this administration has made a bold and historic leap. They have acknowledged alternatives to blind faith in prohibition, that there may be better ways to protect public safety and health, to reduce violence and harm.

As a result, one can now imagine how nearly eight decades of marijuana prohibition will end -- not with the sudden crash of congressional action, but hollowed out from within as states one by one take matters in their own hands.

Today, nearly half of all drug arrests in the country are related to marijuana, overwhelmingly for low-level possession. The guidelines effectively explain how other states can follow Colorado and Washington's lead in regulating commercial marijuana production without federal interference. Many will do just that. More important while some prohibition laws may be left standing, they will decreasingly be enforced. The nearly 750,000 annual possession arrests -- and the noxious racial disparities that notoriously accompany them -- will be greatly reduced.

None of this is of course preordained. Public opinion is evolving quickly in favor of legalizing marijuana, and that will certainly be accelerated by this announcement. But to maximize the new climate, states must act and elected officials must start publicly declaring the support for marijuana legalization they commonly express in private.

With this statement the Obama administration has also created wider reform opportunities. If vigorous marijuana regulation aligns with federal priorities, what other drug policy arenas could states now reasonably explore, some of which defy current federal law? For example they could license supervised injection facilities that are proven abroad to reduce new HIV infections, overdose deaths and public nuisance without increasing drug use or criminal activity. Nearly 100 such facilities operate today in scores of cities around the world.

A consensus already exists that our punitive approach to drugs simply doesn't work. The doorway to effective alternatives is wider than ever before.

Stephen Gutwillig is deputy executive director of the Drug Policy Alliance, the nation's leading organization promoting alternatives to the failed war on drugs.

This piece originally appeared on The Huffington Post.

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