Joshua Green, senior editor of The Atlantic has an interesting post, “Do Marijuana Ballot Initiatives Help Democrats Win?” Green cites the piggy-back strategy used by Karl Rove as a possible template for Dems:

Not long ago, Karl Rove was considered a political genius. His mastery of the small, clever maneuver–typically unappreciated until it swung an election–was a big reason why. To his enemies, nothing exemplified Rovean perfidy like the state ballot initiatives he encouraged banning gay marriage that appeared across the country in 2004. Rove’s idea was that conservatives lukewarm on President Bush could be persuaded to support the ban–and, once they’d shown up to do that, would probably vote for Bush, too. On Election Day, the ballot initiatives passed easily and Bush narrowly won a second term.
…Acting on a tip from an Obama official, I found a few Democratic consultants who have become convinced that ballot initiatives legalizing marijuana, like the one Californians will vote on in November, actually help Democrats in the same way that gay marriage bans were supposed to have helped Republicans. They are similarly popular, with medical marijuana having passed in 14 states (and the District of Columbia) where it has appeared on the ballot. In a recent poll, 56 percent of Californians said they favor the upcoming initiative to legalize and tax pot.

The idea is to re-enthuse the youth base which was so helpful in Obama’s victory. Green quotes Jim Merlino, a Colorado political consultant, who helped pass marijuana initiatives in 2000 and 2006: “If you look at who turns out to vote for marijuana, they’re generally under 35. And young people tend to vote Democratic.”
The pro-legalization constituency undoubtedly can be found to some extent among all age groups, especially the greying generation of the 1960’s. The assumption would be that it might also increase mid term turnout of liberals, who favor legalization, but also libertarians, some of whom vote Republican and perhaps even some conservatives, who realize that minor marijuana offenses account for a substantial percentage of incarcerated individuals and associated expenditures.
Green acknowledges that there is no hard data indicating a clear link between marijuana ballot initiatives and increased Democratic turnout, nor even between same sex marriage ballot initiatives and Republican turnout. But he does cite a study indicating that in the 1982 midterms nuclear freeze initiatives in ten states had “a significant positive effect on Democratic candidates.”
In November up to a half-dozen states may hold ballot initiatives to permit medical patients, and others, to smoke marijuana. In California, which has already legalized marijuana use for medical purposes, voters will decide on legalizing it for adults. The state NAACP has endorsed Proposition 19, arguing that selective enforcement of current marijuana laws disproportionately penalizes people of color.