In a country where, according to one poll, 50 percent of the population believes marijuana should be legal yet no major-party candidate agrees, there's a clear opening for a pro-legalization voice. But there seems to be something deeper than political calculation at work in the way Johnson has championed the issue. Coming out against the drug war, as Johnson did in 1999, early in his second term as the Republican governor of New Mexico, was a deeply formative experience in his political career. It might even be the reason he's running his decidedly upstream campaign today.

When Johnson made his announcement in 1999, he didn't expect it to be a political winner. "I did not do this naively," he told me. His approval rating plummeted 30 points. Condemnations from national political figures, both Republicans and Democrats, rained down. But the response from his constituents took him by surprise. Letters, phone calls, emails, and faxes poured into his office and the local newspaper, 90 percent of them supportive, by his estimate. Going out in public started to feel different, too.

"My first term, 10 people would approach me on the street, and one and a half would get in my face and tell me that I was the scum of the earth," Johnson recalled. "That I hated schoolchildren, that I hated teachers, that I wanted to starve old people, that I was a polluter, you name it. After I came out on this issue, the number of people that approached me on the street went up tenfold, and the number of people that got in my face went to zero. And I attribute that to, 'Gosh, if he's saying this about drugs, obviously he's not a polluter. He can't be anti-human being.'" By the time he left office, Johnson's approval rating had mostly rebounded.

It's largely because of this history that Johnson has credibility among the libertarians whose movement he's now joined. The party's 2008 nominee, former Rep. Bob Barr, was a onetime drug warrior who claimed to have seen the light -- but since getting less than 1 percent of the national vote, Barr hasn't had much to do with his onetime Libertarian Party allies, and in the 2012 primaries he endorsed Newt Gingrich. Libertarian activists are always looking for standard-bearers who can claim some electoral legitimacy, but the experience with Barr left them feeling used. Johnson doesn't command the same following as Rep. Ron Paul, who has declined to anoint him as a successor. (Paul told Reason last week that Johnson "certainly has a lot of libertarian views," but people should make up their own minds.) But the fact that he embraced drug legalization while still a sitting Republican governor helps persuade the Libertarian Party diehards that he's not just another opportunist seeking a ballot line.

Johnson's experience taking on the drug war also seems to have taught him a couple of key things that still mark him as a politician: that he can trust his political instincts, and that it's possible to forge unorthodox coalitions of liberals and conservatives outside the current partisan paradigm. That's what he's trying to do on the national level today.