WASHINGTON — As polls show record support for marijuana legalization, advocates say the midterm elections could mark the point of no return for a movement that has been gathering steam for years.

"The train has left the station," said Rep. Earl Blumenauer, D-Ore., a leading marijuana reform advocate in Congress. "I see all the pieces coming together... It's the same arc we saw two generations ago with the prohibitions of alcohol."

Voters in four states will weigh in on ballot initiatives to legalize weed for recreational or medical use next month, while voters everywhere will consider giving more power to Democrats, who have increasingly campaigned on marijuana legalization and are likely to advance legislation on the issue if they win back power in Congress and state capitals.

It's been just six years since Colorado and Washington became the first states in the country to legalize marijuana, but in that short time span, seven other states and the District of Columbia have followed. Thirty states have legalized medical cannabis. The entire country of Canada legalized the drug last week.

Politically, the issue has gone from a risible sideshow to a mainstream plank with implications for racial justice and billions of dollars in tax revenue. "Politicians embraced it because it's actually good politics,” said Blumenauer. “They can read the polls.”

Two out of three Americans (66 percent) now support the legalization of marijuana, according to a new Gallup survey, including a majority of Republicans and, for the first time, a majority of voters over the age of 55. Not surprisingly, support is strongest among Democrats (75 percent) and young adults between the ages of 18 and 34 (78 percent).

But opponents say advocates are ignoring the backlash that rapid legalization has created, including from some surprising corners, like the Detroit chapter of the NAACP, which is set to announce Tuesday its opposition to a ballot measure that would legalize marijuana in Michigan, the most significant of this year's referendums.

Michigan already has a robust medical marijuana industry, but voters could decide to fully legalize the drug for recreational use on Nov. 6. A recent survey commissioned by The Detroit Free Press found 55 percent of voters supported the measure, compared to 41 percent who opposed it.

Meanwhile, North Dakota voters will also have a chance to legalize recreational marijuana in one of the most conservative states in the country, two years after 64 percent of voters approved its medical use during the 2016 election. Advocates are less hopeful about their prospects this year, though a pro-legalization group released a poll this weekend claiming a narrow 51 percent of likely voters approve of the measure.

Utah, a deep red state with some of the strictest alcohol rules in the country, is considering a medical marijuana initiative, which polls suggest is favored to succeed, even though most of the state’s political and religious leaders oppose it.

At the same time, Missouri voters will consider three separate and competing medical marijuana ballot initiatives. The situation has frustrated advocates and could confuse voters, especially because it's unclear what will happen if they approve more than one next month.

Meanwhile, Vermont's state legislature earlier this year legalized cannabis, though not for commercial sale, and New York and New Jersey could be next, as lawmakers in both states are actively considering the issue.

“The tipping point probably passed one or two election cycles ago,” said Tom Angell, an advocate and journalist who founded the news site Marijuana Moment. “It keeps becoming more and more apparent that it will be impossible for prohibitionists to reverse our gains. And as a result, more mainstream politicians are getting on board.”

Progressive Democrats like Florida gubernatorial candidate Andrew Gillum and Texas Senate candidate Rep. Beto O’Rourke, D-Texas, have adopted marijuana legalization as a central plank of their campaigns by tying the issue to criminal justice reform, citing the disproportionate number of African-Americans arrested for the drug even though usage is common among whites.

In one of the biggest applause lines of his stump speech, O’Rourke — a longtime advocate of marijuana reform dating back to his days on the El Paso City Council — asks supporters who will be the last person of color incarcerated for possessing something that is now legal for medical use in a majority of states.

But a growing number of more mainstream Democrats have adopted the policy too, like J.B. Pritzker, the billionaire hotel magnate running for governor of Illinois, and Michigan gubernatorial candidate Gretchen Whitmer, who beat a progressive Bernie Sanders-style challenger in the Democratic primary.

“Democrats have really jumped on this as a way of galvanizing their voters,” said Michael Collins, the interim director of the pro-legalization group Drug Policy Action. “If you're on the more moderate side of the party and you want to show your progressive bona fides, you go to marijuana, because it's not as controversial an issue as, say eliminating ICE,” the Immigrations and Customs Enforcement agency.

That’s quite a shift from just a few years ago, Collins said. “I remember not even being able to get meetings in the Senate,” he said.

It can also be a windfall for states who need to meet spending demands, but are loathe to raise taxes.

Democrat Phil Murphy, elected governor of New Jersey last year, made marijuana legalization a top priority, hiring as his chief of staff the former head of a marijuana business organization and including an estimated $60 million in new tax revenue from marijuana in his first state budget proposal.

But Kevin Sabet, a former adviser to the Obama administration on drug policy who runs a group that opposes marijuana legalization, says advocates are overstating the inevitability of their side.

“I don't think this is a done deal at all,” he said, noting that his group, Smart Approaches to Marijuana, has raised more money this year than any year in its history. “Ironically, the more legalization rolls out, as recklessly as it is, the more support we get.”

Polls showing sky-high support for legalization can be misleading, Sabet argues, because they use vague wording that can lead respondents to conflate decriminalization with a full-blown recreational system that allows for storefront dispensaries.

Some of the most vocal opposition, he said, has come from African-American organizations, who express concern that the commercialization of the marijuana industry has primarily benefited white entrepreneurs even though communities of color have borne the brunt of the drug war.

"This really isn't about social justice, it's about a few rich white guys getting rich," Sabet said, noting that the black caucus in the New Jersey state legislature has helped stall Murphy's legalization effort in New Jersey.

Proponents acknowledge the racial disparities in the marijuana industry, and some, like Maryland Democratic gubernatorial candidate Ben Jealous, the former head of the NAACP, has advocated a legalization regime that would benefit black and brown weed entrepreneurs.

Either way, if Democrats win back the House, advocates say Congress could advance a number of reform bills that have been blocked by the Republican majority.

Some, like a bill to exempt states that have legalized marijuana from federal restrictions and another to allow marijuana businesses to use banks, have numerous Republican co-sponsors and could pass both chambers of Congress today — if only leaders allowed lawmakers to vote on them, advocates say.

"There's legislation teed up and ready to go," said Blumenauer, who wrote a memo to Democratic leaders laying out an agenda he hopes they will adopt if the party regains power. “These are things that will not get in the way of other work we have to do.”