SACRAMENTO — As they come of age and register to vote, millennials–that enormous generation born since 1981–are surging so fast they’re on the verge of overtaking the baby boomer behemoth as a share of the California electorate. And new evidence confirms that, so far at least, the GOP is losing them.

Fewer than 20 percent of millennial voters in California are registered as Republicans. Not that the Republicans’ loss is the Democrats’ gain. Recent voter data shows that millennials are the driving force behind the huge growth in Californians registering with no party affiliation at all.

They’re also more optimistic than other generations: The latest polls show them more approving than their elders of the job the Legislature is doing. And they’re far more supportive of the direction in which California is headed.

Their emerging dominance means that 20- and 30-somethings are well-positioned this year to influence several critical questions — including the generational changing-of-the-guard as two Democrats compete to replace retiring U.S. Sen. Barbara Boxer, as well as the fate of 17 ballot measures covering issues as varied as the death penalty, gun control and marijuana.

As for the state issue over which millennials are most likely to visibly wield their power, many people point to Proposition 64, the initiative to legalize recreational use of pot. That was the prediction of Rep. Eric Swalwell, D-Dublin, as the millennial lawmaker told a recent UC Berkeley conference focused on the generation. “So I hope young people show up” to vote “because once California legalizes marijuana, I think the rest of the country is going to follow,” he said.

Millennials today make up 29 percent of the state’s registered voters, the second largest share among five living generations. Only baby boomers, at 32 percent, make up a bigger bloc — for now.

“You’ve got to think of millennials as essentially becoming the largest single segment of the electorate,” said Paul Mitchell, vice president of Political Data Inc., which analyzed recent California voter registration data by generation.

Their dominance among California registered voters has been climbing steadily since the generation hit voting age in 2000. This spring, tech-savvy millennials propelled a surge in voter registration: Nearly 200,000 Californians signed up to vote over two days in May when a Facebook campaign linked users to the state’s online registration portal — and nearly two-thirds of them were 35 or younger, according to Secretary of State Alex Padilla.

Now other tech companies are expressing interest in promoting voter drives on their platforms, potentially further boosting registration among millennials before the November election. Padilla said he’s in talks with Google and Twitter.

“It’s great to see the social media world really committing to this,” he said. “It’s really helpful and powerful.”

How potent this generation really is at the polls comes down to one question: Will they actually vote? Though young people typically have low turnout rates, they could be more motivated this year by the turbulent presidential election, which then would have a spillover effect on California races with long-lasting implications.

“If they vote, I think they will be significant in any number, if not all, of the initiatives,” said Gale Kaufman, a political consultant running campaigns for Proposition 64 to legalize marijuana, as well as Proposition 55 to extend income taxes on the wealthy. “Issues like guns, the death penalty and marijuana should evoke a lot of interest at the campus level and moving through millennials. Social issues or values issues tend to energize younger voters.”

Opponents of marijuana legalization plan to deploy a campaign designed to raise concerns about specific aspects of Proposition 64, especially those that could be salient to parents.

“I think the concept polls well; I don’t think the details poll well,” said Andrew Acosta, a political consultant working on the campaign against Proposition 64. “Once you start to open this thing a little bit, there might be things that turn people off.”

Still, many millennials have their minds made up. Voters age 18 to 34 favor legalizing marijuana by 2 to 1, far greater than older voters, according to a Public Policy Institute of California poll in May.

Hours before Swalwell passionately endorsed Proposition 64 in Berkeley, one conference participant said it was the only initiative on California’s long ballot this year that he was aware of–and he plans to vote “yes.”

“We’ve had medicinal marijuana in California for about 20 years,” said Chris Johnigan, 29, a substitute teacher who lives in the Bay Area. “It seems like we’re past due to have it legalized on a recreational level.”

Marijuana legalization may be the first issue in which millennial voters cast the decisive votes in California. But it certainly won’t be the last.

CALmatters is a nonprofit journalism venture dedicated to exploring state policy and politics.