Let's talk seriously today about marijuana, without the requisite jokes about hippies and munchies.

The nonpartisan Pew Research Center has released a new survey that speaks for itself: "For the first time in more than four decades of polling, a majority of Americans favor legalizing the use of marijuana."

This historic finding - 52 percent yes, 45 percent no - is proof that what was once deemed marginal is now mainstream. Much like the issue of gay marriage, legal weed is a grassroots movement incubated at the state level, and it will only grow stronger over time as resistant older voters make way for the young.

But, on at least one pot policy front, the future is now. The Pew poll - which shows an 11-point surge in national support for legalization since 2010; and a 20-point surge in support since 2002 - merely confirms what Colorado and Washington State have already done. Last November, the voters said yes to legal marijuana; in Colorado, marijuana's winning margin was larger than President Obama's. Both states are currently working out their regulatory regimes, plus all the distribution and retail details.

And, perhaps most importantly, they're still waiting to see whether Washington will slap them down.

Lest we forget, the voters in those states defied federal law when they legalized marijuana - because the drug is still verboten, a scourge of society, under the terms of the 1970 Controlled Substances Act, which puts it in the same no-no category as heroin.

It's the old American conundrum: When should the feds intervene and trump state policy? When is "state's rights" a noble doctrine, and when is it not? Fifty years ago, the feds found southern segregation to be ignoble, but do they feel that way about pot? They're well within their rights to preempt the states, to threaten the marijuana growers and distributors with federal prosecution. The Justice Department signaled months ago that it would indeed ender an official opinion, although Obama has hinted that the feds favor a benign response ("we've got bigger fish to fry"). But that's as much as we know.

If public opinion means anything, Washington would be wise to ease off and let the state experiments play out. The ascendent voters - young people, aged 18 to 29 - are driving national opinion. Sixty four percent say yes to legalization (a six-point jump since 2010). But Pew reports even sharper spikes in the other age categories. Among voters aged 30 to 49, 55 percent say yes (a 13-point jump since 2010). Among voters aged 50 to 64, 53 percent say yes (a 13-point jump), and even though support remains low among voters 65 and older, the current 33 percent yes camp is 11 points larger than it was in 2010. The elderly yes share is bound to increase as more Baby Boomers flood the ranks.

Message to feds: Back off

But here's the key Pew finding: Most Americans want the feds to leave Colorado and Washington State alone. It's yes to legal state marijuana, no to federal meddling. Among swing-voting independents, 64 percent say the Justice Department shouldn't try to enforce the federal prohibition. Among Democrats, it's 59 percent. And among Republicans, this share is nearly as high - 57 percent (fueled, no doubt, by the leave-us-alone libertarians, and the state-sovereignty adherents of the 10th Amendment).

So what we have here, amazingly enough, is bipartisan agreement on a cutting-edge social issue. How often does that happen in polarized America?

Actually, that's happened with gay marriage. And, much like gay marriage, the marijuana legalization energy is being generated at state level - in the so-called "laboratories" of democracy (as coined by Louis Brandeis). Eighteen states have legalized medical use, including New Jersey, and seven more are weighing it. And at least four states - Oregon, Alaska, Maine, and California - are likely to put legalization-and-regulation measures on the ballot by 2016. (Pennsylvania is a non-starter, even for medical use, as long as Gov. Corbett and the Republican legislature remain in power.)

Granted, Colorado and Washington State have a lot of stuff to sort out - like determining how pot will be taxed (akin to alcohol), grown, and sold; and how pot should be policed (what happens if cops stop a bad driver and it turns out he's driving while high?). As for the feds, they do have a short-term interest in ensuring that legal weed stays within the borders and doesn't migrate to the illegal 48 states. (Just wondering: will the TSA screeners at the Denver airport have to become more vigilant?)

The unknown is always a bit unnverving, but clearly, the bipartisan support for legalization is a thumbs-down vote for the status quo. The prohibition policy has become a national joke. According to the FBI, over 660,000 Americans were arrested in 2011 for possession of marijuana. A study by the libertarian Cato Institute says that the enforcement of federal marijuana laws, including incarceration, carries a minimal annual price tab of $5.5 billion. That seems like a waste of taxpayers' money, with respect to a drug that could actually generate billions in tax revenue.

If the nascent reforms in Colorado and Washington State - and the grassroots opinion, as tracked by the Pew poll - spark a reassessment of national policy, we'll all be better off.