Taken together, this year's marijuana surveys suggest that Americans have grown even more bullish on the prospect of legal weed than they were in 2014. Pictured: Harmony Johnson of Boulder is decked out for Denver's annual weekend 4/20 festival at Civic Center Park on April 19, 2015. (AAron Ontiveroz, Denver Post file)

Are Americans more bullish than ever on marijuana legalization?

Just two years ago, the public was evenly divided on marijuana legalization, according to polling from the Public Religion Research Institute: In August 2014, 44 percent of Americans favored it, while 50 percent were opposed.

That 44 percent was on the low end of the support recorded in similar polls taken at the time. That fall, 51 percent of respondents told Gallup they supported marijuana legalization. Around the same time, 52 percent said the same to Pew.

But the latest poll from PRRI shows a stunning jump: 63 percent of Americans said they support making marijuana legal. In the September poll, 31 percent of respondents said they “strongly” supported legalization. Just over one-third of Americans – 36 percent – now say they oppose legalization, with only 17 percent opposing “strongly.”

The 63 percent in the PRRI survey represents the highest level of support for marijuana legalization of any survey fielded this year, or indeed ever. An AP-NORC survey conducted in March found 61 percent support. Earlier this month, a Gallup poll showed 60 percent support.

Taken together, this year’s marijuana surveys suggest that Americans have grown even more bullish on the prospect of legal weed than they were in 2014, when the first retail pot shops opened in Colorado and Washington state and voters in Oregon, Alaska and Washington, D.C., opted to follow suit.

The PRRI survey, like the others, also suggests that legalization opponents are winning over conservative Republicans who have traditionally been skeptical of the merits of legalization. Nearly half of likely Trump voters – 48 percent – say that they support making the use of marijuana legal. Seventeen percent of Trump supporters feel that way strongly. As recently as last year, fewer than 40 percent of Republicans told the Pew Research Center they supported marijuana legalization.

Five states are weighing whether to embark on marijuana legalization themselves. As I wrote last week, strong support for legalization nationally doesn’t necessarily translate to easy victories for specific marijuana proposals on the ballot.

For instance, PRRI and the other pollsters typically ask respondents whether they think the “use” of marijuana should be made legal. A person may support the idea of smoking pot in the privacy of one’s home without police interference, but may nonetheless balk at proposals that would create a commercial marijuana industry selling retail marijuana products, as this year’s state ballot initiatives do.

Still, with three national surveys this year showing 60 percent or greater support for legalization, it seems that public attitudes have reached some sort of tipping point. From a governing standpoint, it may become increasingly difficult for policymakers to maintain a strict prohibition that nearly two-thirds of citizens oppose.

One problem is that a widely opposed prohibition – 33 million American adults currently use marijuana, according to Gallup’s estimate – makes scofflaws out of millions of otherwise lawful citizens.

“The fruitless efforts at enforcement are creating public disregard not only for this law but for all laws,” complained Commissioner of Prohibition Henry Anderson in the 1930s. “The courts are cluttered with prohibition cases to an extent which seriously affects the entire administration of justice.”

Anderson’s comments were about alcohol prohibition, but they could just as easily apply to marijuana prohibition today.