Three states are voting today on whether to allow medical use of marijuana — Massachusetts, Montana, and Arkansas — but that's old hat by now. Oregon, Washington, and Colorado are going much further in the push for pot decriminalization, with voters deciding on whether to make pot legal for recreational use (the drug would be regulated and taxed like alcohol). Californians considered and rejected a similar initiative in 2010, but chances are good that at least one of these three states will pass its measure on Tuesday. If so, whoever wins the presidential race would have to decide how much to enforce federal laws against marijuana use — which gives decriminalization advocates a pretty big stake in the headline race. Here's a look at what Oregon, Washington, and Colorado voters will decide, and where President Obama and GOP challenger Mitt Romney stand on the issue of legalizing pot.

What's on the ballot?
Washington's Initiative 502, Colorado's Amendment 64, and Oregon's Measure 80 would all allow people over 21 to buy marijuana for recreational use, and license, tax, and otherwise regulate the drug along the same lines as alcohol. Washington's proposal would levy a 25 percent tax on sales from grower to processor, processor to retailer, and retailer to purchaser, and would create tough rules against driving under the influence of pot. Colorado would allow retailers to apply for licenses to sell pot. Oregon's proposal is similar, but unlike the other two, places no limit on how much marijuana you can grow and sell.

What are the pros and cons?
Advocates of decriminalizing marijuana, including some law enforcement officials, say busting people for pot is an expensive waste of scarce resources, and the tax revenue could help fill depleted state coffers. They also point to a recent study from a Mexico City think tank, the Mexican Institute for Competitiveness (IMCO), which found that the three state measures could "deal a blow to Mexico's traffickers of a magnitude that no current policy has got close to achieving," depriving the cartels of $1.4 billion of their $2 billion in annual marijuana income, from the U.S. (once you factor in the potential for these states' legal pot to filter out to other states), says Tom Wainwright at The Economist. "The stoned and sober alike should bear that in mind when they cast their votes on Tuesday." Opponents argue that pot is addictive in itself and acts as a gateway drugs to harder, more destructive substances.

Which states might pass the recreational pot measure?
Washington and Colorado are the most likely — a recent KCTS-9 Washington poll pegged support for Initiative 502 at 55 percent versus 38 percent opposed, and an Oct. 9-10 Denver Post poll found Amendment 64 winning, 48 percent to 43 percent. In Oregon, the measure didn't get on the ballot until later than in the other states, and it appears headed for defeat — an October 25-28 poll for The Oregonian found voters opposing Measure 80 by 49 percent to 42 percent. But even positive polling doesn't mean passage is assured, says William M. Welch at USA Today. "Both sides are aware of what happened in California," where Prop 19 lost by six percentage points after leading in the polls.

Where does Obama stand on marijuana?
In 2004, Obama — who has copped to smoking pot in his younger days — backed loosening marijuana laws during a Senate debate. "The war on drugs has been an utter failure," he said. "We need to rethink and decriminalize our marijuana laws. We need to rethink how we’re operating the drug war." In 2008, he suggested he'd treat medical marijuana patients with kid gloves. In April 2012, however, he said at a summit of Latin American leaders, "I don't think that legalization of drugs is going to be the answer." And after two years of not meddling with medical marijuana, U.S. attorneys started cracking down on big medical marijuana dispensaries in California and Colorado — a move many legalization advocates viewed as a betrayal.

How about Romney?
Romney has been pretty consistent in his opposition to decriminalizing marijuana. "I would not legalize marijuana for medicinal purposes," he said in July. "The idea of medical marijuana is designed to get marijuana out in the public marketplace and ultimately lead to the legalization of marijuana overall.... If you elect me president, you're not going to see legalized marijuana. I'm going to fight it tooth and nail." He was just as explicit as late as Oct. 1. "I oppose marijuana being used for recreational purposes," he said. "I believe federal law should prohibit the recreational use of marijuana."

Where does the public stand?
Support for decriminalizing marijuana certainly seems to be growing. In October 2011, Gallup found half of respondents backing the legalization of pot, versus 46 percent opposed — the highest level of support since Gallup started asking about legalization in 1970 — and a February 2011 YouGov poll for The Economist found 58 percent supporting the taxing and regulating of weed like alcohol, versus 23 percent opposed with 19 percent undecided. "Public opinion is trending in this direction,'' John Matsusaka, president of the Initiative & Referendum Institute at the University of Southern California tells USA Today. "It's a matter of time before one of these passes.''

So what's a pro-pot voter to do?
There are two unabashedly pro-legalization advocates on the ballot in most states — Libertarian Gary Johnson and Green Party candidate Jill Stein — but some advocates of decriminalization want to back a candidate who might win, and they're divided. Dilbert creator Scott Adams, for example, is so disgusted with the Obama administration's crackdown on medicinal pot dispensaries that he's backing the challenger. "Romney is likely to continue the same drug policies as the Obama administration," Adams concedes. "But he's enough of a chameleon and a pragmatist that one can't be sure. And... he is vocal about promoting states' rights, so he's got political cover for ignoring dispensaries in states where medical marijuana is legal." That's dumb, argue the editors of CelebStoner. Obama has at least supported marijuana decriminalization, while "Romney would send us back to the dark ages when reform was not on the table." Besides, Obama "has been known to change his tune on controversial issues (see his stance on gay marriage)," and he could see the light on decriminalizing pot, too. 

Sources: AP, BloombergBusinessweek (2), CelebStoner, Christian Science Monitor, Economist, Gawker, Oregonian, Politico, Reason (2), Reuters, Salem Statesman Journal, USA Today