Legalizing marijuana is an issue made to order for the Democratic Party. A majority of Americans now supports the idea, and so do two out of three Democrats. Two states have done it, and several more may vote on it in 2016.

The party could put the issue to use against Republicans, who have no desire to be the party of weed. Can you imagine Rick Santorum or Marco Rubio or Paul Ryan endorsing legalization? Even libertarian Rand Paul declines to go that far.

He is not misreading his party. Chris Christie will lose no votes in the primaries for saying, as he did last month, "I don't favor legalization. I don't favor recreational use. I don't favor decriminalization. And I don't favor the use of marijuana as a medicine."

So the GOP is locked into a position that is steadily losing appeal with the public. Worse yet, support for legalization is highest among young people and lowest among seniors. Rejecting it is a great way to worsen the Republicans' ominous demographic problem.

There's only one thing standing in the way of the Democratic Party using the pot issue to win elections, curtail arrests of minorities, free money for social programs and cement the allegiance of young voters: Democratic politicians.

Start with Hillary Clinton. Her husband may have tried weed, but she has never attested to such youthful indiscretions, probably because she never committed them. As secretary of state, she spoke out against legalization of cannabis, and in 2008 she rejected even decriminalization.

That stance is no accident. Clinton got involved in politics in the 1970s, when Democrats were tarred as hippies and draft-dodgers—embracing "acid, amnesty and abortion," Republicans alleged. If Democrats of that era learned anything, they learned to look and sound like they couldn't find Woodstock on a map.

Shedding an ingrained persona at her age does not come easy. My bet is you'll see Dick Cheney on a skateboard before you'll see Clinton go after the stoner vote. If she's the 2016 presidential nominee, legalizers will have to look elsewhere.

Democratic governors also blanch at the sight of a pipe. New York's Andrew Cuomo, who only recently accepted medical marijuana, rejects legalization. Connecticut's Dannel Malloy says, "I don't think we are ready, or want to go down that road."

Don't look for a live-and-let-live approach in California, where Gov. Jerry Brown recently went off on the sort of addled tangent that could be excused only if he were high. "All of a sudden, if there's advertising and legitimacy, how many people can get stoned and still have a great state or a great nation?" he asked scornfully. "The world's pretty dangerous, very competitive."

Brown apparently is unaware that cannabis use is far more common in the United States than in the Netherlands, which has one of the most permissive regimes in the world. Banning pot doesn't actually prevent people from getting baked.

Of course, if you truly wanted to worry about a mind-altering toxin that damages productivity and ruins lives, you wouldn't focus on marijuana; you'd focus on alcohol. But Brown doesn't worry that the Golden State's many wineries and craft breweries put it at a competitive disadvantage.

Even Democratic governors presiding over legalization are not wearing "Bong Hits for Jesus" T-shirts. When Washington voters voted on legalization in 2012, Jay Inslee was running for governor and unsuccessfully opposed it. Colorado's John Hickenlooper came out against the Colorado initiative, which also passed. Neither has gotten giddy about the idea since then.

But it's hard for Democrats to justify treating mere possession as a crime, if only because that policy has so many corrosive effects they should care about. It squanders revenue that could be used for more useful government programs. It causes blacks to be arrested four times more often than whites, even though they smoke weed at roughly the same rate.

It encourages police to stop and frisk—a practice that in New York City, a federal judge ruled last year, led to violations of the Constitution and unjustified racial profiling.

Democratic politicians could be making the case for change at a time when the public is increasingly receptive to a new policy. Instead, they are clinging blindly to the status quo. They undoubtedly are smarter than the average rodent. But even rats know enough to leave a sinking ship.