When Keith Stroup joined the movement to legalize marijuana in the early 1970s, just 12 percent of the American public supported legalization.

Today, polls show that a majority of Americans support legalization, and in the past four years four states and the District of Columbia have legalized recreational pot.

“We’ve made an incredible leap in support, but it has been slow and gradual,” said Stroup, who founded the National Organization for the Reform of Marijuana Laws, one of the country’s leading pro-legalization groups. “Now I think we’re beginning to accelerate.”

READ MORE: Your 2016 election survival guide

As Election Day draws near, the plethora of marijuana-related initiatives on state ballots across the country highlight the gains made by NORML and other legalization groups in recent decades.

Measures to legalize recreational marijuana are on the ballot in five states this year: California, Nevada, Arizona, Maine and Massachusetts. Four other states — Florida, Arkansas, North Dakota and Montana — are considering initiatives to legalize medical marijuana, a move that some say is a first step towards full legalization.

The potential for a major shift in marijuana policy has spurred opponents to pour millions of dollars into state campaigns to block the legalization initiatives.

If a majority of the ballot initiatives pass, pressure would mount on the federal government to end its roughly 80-year prohibition of pot. The potential for a major shift in marijuana policy has spurred opponents to pour millions of dollars into state campaigns to block the legalization initiatives.

Both sides agree that the lynch pin is California, where medical marijuana has been legal since 1996. The state, which has the largest economy in the U.S., is often on the forefront of social and economic change.

Legal marijuana sales nationwide jumped to $5.4 billion last year, an increase from $4.6 billion in 2014, according to a study by ArcView Market Research, which produces an annual report on the cannabis industry.

In the event that California votes yes on Proposition 64 and legalizes marijuana, the national pot industry would triple in size, and eventually grow to $50 billion by 2026, a report by the research group Cowen & Company found.

Carla Lowe, the head of Citizens Against Legalizing Marijuana, a group that is fighting the state’s legalization initiative, said the vote in California would have an out-sized influence on the rest of the country.

“If California votes for the legalization of pot for fun, so goes the nation,” Lowe said.

Californians rejected a ballot measure to legalize recreational pot in 2010 by a vote of 53 to 46 percent. A similar measure failed to make the ballot in 2012. This year, supporters have raised about $22 million to back Prop 64. A third of the money has come from a single donor, Napster co-founder and former Facebook president Sean Parker. Opponents of Prop 64 have spent approximately $2 million.

In addition to raising more money this time around, the state’s pro-legalization groups have also tweaked their argument to focus on the economic benefits of bringing a shadow industry above ground. The strategy is aimed at voters who may not use marijuana, but remain concerned about the state’s economy.

“Right now there’s an estimated $12 billion spent on marijuana in California that’s un-taxed,” said Ben Bradley, the operations director of the California Cannabis Industry Association. Legalizing recreational pot would “bring in over $1 billion [in state revenue] in the first year,” he added. “That would be immensely helpful for the state budget.”

Under the proposal, supporters say, the revenue generated by legal marijuana sales would go to substance abuse treatment, education programs and other services.

Opponents contend that the ballot measure is designed to benefit large-scale marijuana growers and industry special interests, while harming small businesses that would get cut out of the legal pot market by corporate competitors.

“The winners are going to make a lot of money on this, and the smaller dispensaries are going to be gobbled up by the Starbucks of marijuana.”

“The winners are going to make a lot of money on this, and the smaller dispensaries are going to be gobbled up by the Starbucks of marijuana,” said Andre Acosta, the campaign spokesman for No on Prop 64, an opposition group.

Critics also argue that the measure, which runs to 62 pages, is too broad, and goes much farther than legalization initiatives that passed in other states.

Prop 64 includes a provision that allows for home delivery services, and television advertising for marijuana products, something that critics strenuously oppose. And perhaps most importantly, the initiative would not give municipalities control over marijuana laws, meaning that cities and towns could not choose to ban the drug at the local level.

That stands in contrast to Colorado and Washington, which both included a local control provision in the recreational marijuana initiatives that passed in 2012.

Since legal pot sales started in Colorado in 2014, roughly 70 percent of the state’s municipalities have approved bans on commercial marijuana operations. Opponents in California said that local opposition, along with studies showing an uptick in emergency room visits by pot smokers in Colorado, should give voters in the Golden State pause.

“It’s going to be a mess,” Acosta said. “I think Colorado is showing that you probably should take a breath, and get some data in place to see how you start and do this the right way.”

Beyond California, the debate around marijuana legalization has also focused on public health and criminal justice policy.

In Florida, supporters have mounted a vigorous campaign to pass Amendment 2, a ballot initiative that would legalize medical marijuana through a constitutional amendment. Under Florida law, the measure needs a supermajority of 60 percent support to pass.

Karen Seeb Goldstein, the executive director of NORML’s Florida chapter, said supporters are focusing their efforts on convincing the public that medical marijuana could be regulated and lead to better patient outcomes for people suffering from Parkinson’s, cancer and other diseases.

“It’s a health issue,” said Goldstein. Medical marijuana “should be made available to patients who need it.”

Goldstein and other supporters pushed back on some health studies that have shown that pot can have a negative impact on brain development, especially among younger users. If voters approve the ballot initiative, Goldstein said, legalization advocates would push for regulations to ensure that the drug does not get into the wrong hands.

“No one is promoting medical or recreational use for teenagers and young people” unless they have a chronic illness, she said.

Elsewhere, proponents argued that legalizing marijuana would allow law enforcement authorities to shift resources away from prosecuting first-time, nonviolent drug offenders, and put the funding toward community policing programs and other much-needed reforms.

“What we’ve been doing doesn’t work. The war on drugs has failed,” said Matt Allen, the American Civil Liberty Union’s field director for Massachusetts, one of the five states considering a ballot initiative to legalize recreational marijuana. “It has continued to create criminal records, and they’re a barrier to education, housing and employment.”

Between 2008, when Massachusetts decriminalized marijuana, and 2014, the number of arrests for pot possession dropped by 93 percent, according to a report by the state’s ACLU office. And yet in 2014, African-Americans were arrested for marijuana possession at a rate 3.3 times higher than whites, even though pot use is consistent across racial and ethnic groups.

Michael Hussey, the president of the Massachusetts Association of Criminal Defense Lawyers, said that legalizing marijuana is consistent with the state’s “commitment to ensure justice and due process.”

“Our long experience with the criminalization of marijuana leads us to the conclusion that the law prohibiting marijuana possession cannot be enforced in a non-discriminatory way,” he said.

Nevertheless, some law enforcement officials said that legalizing medical or recreational pot posed a public safety concern. Andy Riner, a state prosecutor in Arkansas, which is considering a measure to legalize medical marijuana, said he was concerned that loosening the restriction on a federally banned substance would hurt communities in his state.

“It’s just a Pandora’s box,” Riner said. Increasing the public’s access to marijuana would constitute “a fundamental change,” he added.

Polls on the different marijuana initiatives show tight contests in California, Arizona and several other states.

People on both sides of the debate are prepared for an intense final stretch of campaigning before Nov. 8. Polls on the different marijuana initiatives show tight contests in California, Arizona and several other states.

Supporters said they were confident that, even if some of the measures fail, the nation would take a major step toward legalization. Betty Aldworth, the executive director of Students for Sensible Drug Policy, said the 2016 election represents “an inflection point” in the debate over pot.

“I’m hopeful that California will pass Prop 64. I expect that a handful of other states will pass as well,” Aldworth said. “But I don’t think if a handful of states fail we should consider that a failure of the fundamental argument against marijuana prohibition.”

“What we see across the board is a continuing growth in support among Americans,” she added. “A rapidly growing number of people support ending prohibition.”