"We assumed that when social change like this begins to happen, that it probably accelerates and continues right on through," Stroup says. "Obviously, we were quite mistaken."

Instead, the 1980s heralded the modern War on Drugs, when federal expenditures on the project skyrocketed, First Lady Nancy Reagan dove in with her "Just Say No" campaign, and the imperative of disrupting the drug trade began to creep into American foreign policy. The national mood shifted so profoundly that one of President Reagan's own Supreme Court nominees, federal Judge Douglas H. Ginsburg, withdrew from consideration after it emerged that he had smoked pot in college and as a law professor in his 20s.

But for the first time in decades, legalization advocates see a light at the end of the tunnel again. "There's been a sea change," says Earl Blumenauer, the Democratic congressman from Oregon who, as a state legislator in 1973, helped push through America's first decriminalization law. "I'm absolutely convinced that in the next four or five years, it's going to pass the point of no return," he told me, after which the federal government is likely to decide to treat the drug more like alcohol, passing tax-and-regulate legislation after the states force its hand. While he's on the sanguine end of the spectrum, the fact remains that even if the states are the ones moving fastest on this issue, the tone in Washington has shifted, too.

"It's become a respected constituency," a once-pessimistic Democratic congressional aide whose boss backs reform told me of the legalization crowd. "If you're a member of Congress you can take a drug reform stance and it's not going to hurt you." This was perhaps best illustrated by pro-reform challenger Beto O'Rourke's primary victory over eight-term incumbent Democratic Rep. Silvestre Reyes last year, despite being savaged on the airwaves in the socially conservative south Texas district for being soft on crime. O'Rourke later won the general election and is now a member of the House.

Looking ahead, the fate of national drug policy rests more than anything else on the behavior of Obama's electorate, or the "coalition of the ascendant" -- young people, blacks, Hispanics, single women, and college-educated whites -- when he is no longer on the ballot. Despite presiding over more medical marijuana raids in his first term than George W. Bush did in two, Obama's emergence has arguably accelerated legalization by drawing these groups into the center of the political conversation. The demographic trends look promising to veterans of the cause, most of whom expect to be able to claim an effective national victory within the next decade as the older voters who remain the fiercest opponents of legalization die and young people who embrace it enthusiastically join the voter rolls.