This is how the opinion on legal marijuana in the US has changed.

() — Oklahoma voters head to the polls Tuesday to conclude a special election on the legalization of recreational marijuana, potentially becoming the 22nd state to authorize its use among adults.

The vote in Oklahoma, where voters legalized medical marijuana in 2018, reflects how the issue now transcends politics and geography, as American attitudes on the issue have moderated in recent years.

Recent polls show that a majority of Americans now say they support the legalization of marijuana. As attitudes change, legislators have become more willing to make changes to the issue: five of the seven states that have legalized recreational drinking in the past two years have done so through legislation.

Should the measure pass, Oklahoma would be the latest state to exemplify how policy on the issue has changed, even in traditionally red states. Two decades ago, two-thirds of Americans opposed legalization. This trend has been reversed.

If his measure passes, Oklahoma would be the fourth state with legal recreational marijuana to vote for former President Donald Trump in 2020.

Gallup polls show that most Republicans now support legalization after decades of opposing the idea, reflecting a broader shift in the population.

Oklahoma is one of 37 states, plus the city of Washington, with a comprehensive medical cannabis program, according to the National Organization for Marijuana Law Reform and the National Conference of State Legislatures (NORML and NCSL, respectively, for its acronym in English).

But many provisions for medical and recreational use exist in gray areas. States have written a wide range of laws, from fully legal marketplaces that collect tax revenue to exceptions for specific products.

That piecemeal legal framework is the product of gradual developments across the state as views on the drug have moderated over the past 27 years.

The legalization movement began in earnest after California voters approved medical marijuana in 1996. In 2012, after other states also adopted medical programs, voters in Colorado and Washington were poised to vote for recreational legalization.

By 2022, enough momentum had built for President Joe Biden to order a review of whether marijuana should remain a Schedule I drug. That classification means marijuana has “no accepted medical use” from the point of view of federal view, like heroin.

But advocates remain skeptical of the federal government’s move after decades of inaction.

“If there were to be a tipping point that would influence the federal government or Congress to prioritize this issue, it’s clear that we’ve been past that tipping point for quite some time,” said Paul Armentano, NORML’s deputy director.

However, in the future, more and more states could legalize its use through the work of their state legislatures rather than through ballot initiatives, Armentano said. He noted that the number of states that can still make changes through the electorate is limited.

Of the 21 states and the District of Columbia that have legalized adult recreational drinking, 15 have done so through ballot measures, while the state legislature has enacted seven.

Activists supporting Oklahoma’s legalization measure argue that recreational marijuana sales could bring billions in tax revenue. Of the 21 states where recreational use is currently legal, 19 have levied marijuana taxes since February, according to the Tax Policy Center.

Congress prevented the city of Washington from establishing taxes, and Virginia and Maryland are still in the process of establishing their markets.

“The way states do this can be lightning fast or time consuming,” said Richard Auxier, senior policy associate at the Tax Policy Center. The effectiveness of states like Arizona and Missouri in establishing their legal markets shows that “if you want, you can go from zero to 60 in the blink of an eye,” Auxier said.

In Oklahoma, which already has a strong medical retail market, the transition will likely be quick, said Bridget Hennessey, vice president of public affairs for WeedMaps. This tech startup connects consumers with dispensaries. According to Leafly, another cannabis startup, at least 1,800 cannabis retailers currently operate in Oklahoma.

If Oklahoma becomes the last state to legalize recreational cannabis, it could be followed by Ohio, where voters will take up the issue in November. With the addition of other states that have introduced legalization bills this year, nearly half of the nation’s states and the city of Washington could have a legal recreational drug market in defiance of federal law by the end of the year.

“This is a political and cultural issue that defies all the norms that we have learned in civics classes,” Armentano said.