California will be the key battleground for marijuana legalization next year, experts tell Bloomberg. They say the outcome of the state’s vote on the issue is likely to determine whether most of the nation decriminalizes marijuana for recreational use.

“A lot of eyes are on California,” Gavin Newsom, the state’s lieutenant governor and a supporter of legalization. “It’s very different than almost any other state because of the scale and the magnitude of the change and what it will represent across the country.”

Ballots in at least five states, including Massachusetts and Maine, are likely to have legalization measures in November 2016.

“Legalizing adult use in California would be a worldwide game changer that would dwarf the markets in Colorado, Washington, Oregon and Alaska combined,” said Troy Dayton, Chief Executive Officer of ArcView Group, a marijuana investment and research firm. The company has raised $70,000 to support the ballot measure.

“A state with so much influence and size is very important,” said Kevin Sabet, co-founder of the anti-legalization group Smart Approaches to Marijuana. “We expect a long, drawn-out battle in California — and an expensive one.”

Both sides of the issue say raising donations will be key to the outcome.

California has 39 million residents, more than double the combined size of the states where voters have legalized marijuana—Colorado, Washington, Alaska and Oregon. Medical marijuana was legalized in California in 1996.

California voters rejected a legalization measure in 2010. Supporters say the measure has a better chance in 2016, because it is a presidential election year in which young voters, who are more likely to support legalization, are also more likely to vote.

A recent poll found that among likely California voters, 55 percent say they favor legalizing marijuana, while 43 percent want it to remain illegal.