I’ve just returned to my home in Washington, D.C. from a trip to the “other Washington” — specifically, Seattle. My two visits to Seattle in the past month have convinced me that Washington state will probably be one of the first two states to tax and regulate marijuana like alcohol.

In mid-August, I attended Seattle’s Hempfest for the sixth time in seven years. For those who don’t know, Hempfest isn’t your run-of-the-mill marijuana rally. In fact, if it were, I wouldn’t attend. This year’s Hempfest, which was the 19th in 20 years, was the largest yet, with an estimated 300,000 people visiting Myrtle Edwards Park on the waterfront over two days. Each year, Seattle Hempfest is literally the largest marijuana-related event in the world.

And bigger is better; there’s safety in numbers. For two days each August, using, possessing, and transferring marijuana for no remuneration (passing a joint) is legal in the park. For a few years, this policy was an informal understanding between the Seattle police and the 100,000+ people they were serving and protecting. But, in recent years, the higher-ups in the police department have actually directed their rank-and-file not to arrest people at Hempfest for marijuana (unless someone is selling it or pushing it on children).

What events preceded this normalization of marijuana?

In 1998, 59% of Washington state voters passed a medical marijuana initiative; then, in 2007, the Washington legislature instructed the state Department of Health to define a 60-day supply of medical marijuana. In 2008, the Department of Health defined a 60-day supply as up to 24 ounces of usable marijuana and 15 plants at any stage of growth.

On a separate track, in 2003, 59% of Seattle voters passed a local initiative to make marijuana possession the lowest arrest priority for local police. After that, the number of arrests within city limits plummeted, and, in January of this year, the city attorney for Seattle announced that his office would no longer prosecute people for marijuana possession.

Seattle Hempfest both led to — and benefited from — the local 2003 initiative victory, for which my organization, the Marijuana Policy Project, provided substantial funding. For two days each year, Hempfest attendees see what it’s like for the public use of marijuana to be legal: There’s no violence (alcohol is prohibited during the event), and there’s good company and music and speeches. And the police see the same thing — especially the no-violence part.

The police and non-police leave with these observations and tell their friends and colleagues. Over the course of the last two decades, perhaps 1.5 million people — most of whom live in Washington — have witnessed this phenomenon. Quite simply, Hempfest has changed the local culture around marijuana. So it’s no wonder that the 2003 initiative passed, which then led to a more formal policy change with respect to marijuana arrests at Hempfest … and then the whole city year-round.

And now, support for making marijuana legal has broken the 50% threshold in the state. The three most recent statewide polls show that 56% of adults support “making marijuana possession legal” (January 2010), 54% of adults support “allow[ing] state-run liquor stores to sell and tax marijuana” (January 2010), and 52% of registered voters support “removing state civil and criminal penalties for possession or use of marijuana” (May 2010).

The 52% figure is probably the most accurate, because it’s important to survey registered voters — as opposed to all adults — when you’re thinking about supporting a statewide initiative, as MPP is considering doing in Washington state for the November 2012 ballot.

Because there are many supportive young people and independent voters who vote only in presidential elections, it’s vitally important to place difficult-to-pass marijuana initiatives on presidential-election ballots. Indeed, MPP’s initiatives have passed by surprisingly large margins in Massachusetts, Michigan, and Montana during presidential elections, while both of our initiatives in Nevada lost during midterm elections.

If we can agree on an initiative that’s drafted to appeal to swing voters (meaning it can’t be too radical) and it’s placed on the November 2012 ballot, I predict that marijuana will be made legal in Washington state in just 26 months.

And this would be a particularly sweet victory, since Gil Kerlikowske, the White House drug czar, is the former police chief of … Seattle.