The curious thing about watershed moments is that it sometimes isn’t clear they’ve happened until much later. But about the use of marijuana, we can date that moment rather precisely.

Last week, the Pew Foundation – the nation’s leading polling organization for social issues – reported that, for the first time, a majority of Americans support legalizing marijuana for adults.

Pew has been asking these questions for a long time – since the 1970s, after taking over the survey from the once-powerful Gallup organization – and the trend lines are striking, to say the least.

Support for legal marijuana was actually quite low in the 1960s, the reputed era of sex, drugs and rock’n roll, at only 17 percent. It rose during the ’70s, then declined during the Reagan years.

When Bill Clinton was elected president in 1992, having smoked but not inhaled, less than one in five adults favored legalization.

But over the last 20 years, support has risen slowly but steadily until, in 2012, the “approve” line crossed “disapprove,” showing that most Americans are comfortable with legalization. The Colorado and Washington referendum results last November surprised many, but – Pew tells us – they shouldn’t have.

The forces driving favorable numbers for marijuana are almost exactly the same as those for same-sex marriage. Young people, by huge majorities, approve of both propositions. And the now-aging baby boomers have changed their minds. Boomers at first liked the idea of legal marijuana, then, becoming parents, turned against it. But they, too, are now firmly in support, with only older Americans still opposed.

What does this mean? That the political shifts apparent in the 2008 election, and confirmed in 2012, were no fluke. The nation is changing and – as 50 years earlier – its young people are leading the way.

The “War on Drugs” declared by Richard Nixon and pursued, with varying degrees of enthusiasm, by every president since then, has been a truly dismal policy failure.

Whether measured by money spent on law enforcement, millions of people jailed for smoking a naturally occurring, largely nontoxic substance, or lives torn apart, the costs are huge. But the utter failure of the campaign is most aptly demonstrated by the classic capitalist law of supply and demand: Marijuana is cheaper, in constant dollars, now than when the “war” began.

Pew also tells us that 48 percent of Americans say they’ve used marijuana. Here, as in the classic lawyer’s saying, the law is an ass.

It’s not as if addiction isn’t a problem, or that kids’ use of marijuana isn’t a real concern. Developing brains may be far more vulnerable to intoxicating substances, including alcohol, than those of adults.

But making marijuana illegal has done nothing to stem those risks. In fact, it’s done the reverse. Young people often report that marijuana is more available to them than alcohol, thanks to the robust black market.

So the public is speaking, and politicians are – tentatively –- responding. President Obama, who never liked the “war,” says the federal government has “bigger fish to fry” than to make arrests in states opting for legal marijuana. Attorney General Eric Holder hasn’t gotten around to codifying that opinion yet, though he may.

Maine, a few DEA task forces aside, hasn’t had much zeal for the “war.” Possession has been the equivalent of a parking ticket for decades – a young John McKernan sponsored the bill, years before becoming governor – and public tolerance was demonstrated by strong “yes” votes in two medical marijuana referendums.

Promotion of marijuana’s therapeutic value proved a clever strategy – if it helps cancer patients and those with Parkinson’s, can it really have no redeeming value?

Maine could become the third state to embrace legalization. Rep. Diane Russell’s bill, LD 1229, would, according to its title, “Regulate and Tax” marijuana, at $50 an ounce.

The bill hasn’t yet been scheduled for a hearing, and was referred to the Criminal Justice Committee, hardly a favorable venue. On the other hand, it has 33 House sponsors and three from the Senate, mostly Democrats but with a sprinkling of Republicans and Independents.

A wild and crazy idea? Not according to most Mainers. The existing tax on medical marijuana brought in $265,655 last year, and that was with a 5 percent sales tax and a limited number of users. The revenue boost for a state budget leaner than ever before could be substantial and, to wavering legislators, persuasive.

It’s unlikely law-abiding Mainers will troop down to the State House to testify at the eventual hearing. But a letter or e-mail wouldn’t be out of place. Legislators listen to them.

Douglas Rooks is a former daily and weekly newspaper editor who has covered the State House for 28 years. He can be reached at [email protected].