If it passes, Colorado's Amendment 64 would mark a true watershed for the fractious and often hapless legalization movement, a motley crew of potheads, civil libertarians, and billionaires that's been set back many times before but has the wind of public opinion at its back. The Colorado measure is polling ahead, but not comfortably so: A poll commissioned by the University of Denver and released over the weekend found 50 percent of Coloradans in favor of the initiative and 40 percent opposed. With undecided voters tending to default to a "no" vote on ballot questions, the outcome is anyone's guess. (The Washington initiative is also leading in polls, while Oregon's narrowly trails, with nearly a quarter of voters undecided.)

GETTING SERIOUS

With so much at stake this time around, Tvert, a husky, talkative Arizonan with close-cropped brown hair, has had to tone it down, to his great chagrin. For this year's ballot measure, there are no sensational billboards and no shocking hijinks. The T-shirts for the Yes on 64 campaign are so nondescript they could be for a school levy; the yard signs simply say, "Regulation Works." And last week, Tvert watched from behind a row of TV cameras as a bunch of guys in suits, a woman in a ruffled blouse, and former Rep. Tom Tancredo -- Republicans all -- gave their endorsement to the measure, the latest strange-bedfellows moment for this most outsider of political insurgencies.

"Think to yourself, conservatives, who you are siding with -- not just the nanny staters but with the cartels!" said former Republican Rep. Tom Tancredo.

"Think to yourself, conservatives, who you are siding with -- not just the nanny staters but with the cartels!" said Tancredo, his zippered-down black polo shirt revealing a tuft of white-gray chest hair.

Though best known for his hardline opposition to illegal immigration, Tancredo, who ran on a third-party ticket and finished second in the 2010 race for Colorado governor, has always seen marijuana regulation as a states'-rights issue. In each of his 10 years in Congress, he voted for an unsuccessful amendment that would have denied funding to the Justice Department for the interdiction of states' medical-marijuana laws.

In an interview, Tancredo acknowledged he's on the opposite side of the issue from many of his fellow Republicans, but noted that going his own way is nothing new for him. "I feel very, very comfortable where I am, along with William F. Buckley and Milton Friedman," he said, before dashing off to record a radio ad for the marijuana initiative that will play on conservative talk stations.

Since California voters approved medical marijuana in 1996, 16 states and Washington, D.C., have followed suit in a mix of ballot-box and legislative actions. Colorado became one of them in 2000. In 2005, Tvert, having just graduated from the University of Richmond, moved to Colorado and started an organization called SAFER, for Safer Alternative For Enjoyable Regulation, aimed at highlighting the relative safety of pot compared to alcohol.