NADIA LATHAN/CalMatters Want to know who’s who in Republican politics? Look no further than the megadonors bankrolling California’s voter ID initiative.

Illinois billionaire packing supply magnate Richard Uihlein, who has poured tens of millions of dollars into conservative causes, has contributed $17 million to the campaign for Proposition 39 , a GOP-backed ballot measure to require voters to show a driver’s license or other government ID to vote.

Uihlein’s involvement and that of other deep-pocketed Republican donors is a signal that conservatives view Prop. 39 as a test of support for future battleground states in the broader push by President Donald Trump to tighten voter restrictions.

Uihlein is joined by Southern California businessman Steven Bray, who loaned the campaign more than $3 million and gave $50,000 outright. The right-wing political group Reform California , tech entrepreneurs Cameron and Tyler Winklevoss and former Robert F. Kennedy Jr. presidential running mate Nicole Shanahan are also major donors. Combined, they have helped the campaign rake in more than $28 million — $11 million more than their opponents a month from Election Day.

Prop. 39’s supporters argue that requiring ID at polling places will ensure California’s elections are secure, and say the mandate is no different from needing an ID to fly on a plane or buy alcohol. Proponents also point out that 36 states request or require voters to show some form of identification at the polls, according to the National Conference of State Legislatures .

California voters currently need a driver’s license and Social Security number to to vote but not when they cast their ballots. If Prop. 39 passes, voters who mail their ballots would have to write the last four digits of their Social Security or other government-issued number on their ballots.

It’s a long-awaited moment for the state’s weak Republican Party which has fought for decades to put a voter ID measure on the ballot in deep blue California.

Assemblymember Carl DeMaio , a Republican, created Reform California and is spearheading the initiative. The freshman San Diego lawmaker’s group funded the ballot operation that collected more than a million signatures to qualify the measure after similar proposals failed in the Democratic-controlled Legislature.

Common Cause and other voting rights groups that oppose the measure fear Prop. 39 would unnecessarily block from voting citizens who can’t find or don’t have a government-issued ID. They argue that this would disproportionately impact, and unfairly penalize, people who recently moved, changed their last name or are low income — and other groups who historically have supported Democrats. Civil rights advocates also argue the measure is unnecessary because voter fraud is rare.

“You are more likely to be struck by lightning than you are to commit voter fraud in a U.S. election,” California League of Women Voters executive director Jenny Farrell said. “There’s no need to add on these additional burdens and security checkpoints in California.”Despite numerous studies showing there is no widespread evidence of voter fraud in U.S. elections, Claremont McKenna College political scientist John Pitney said such claims have circulated for decades in far-right circles.

Attempts to constrict voter laws through ballot measures have increased in some states ever since the expansion of voting rights to African Americans during the Civil Rights Movement.

But fears about voter fraud accelerated during the first Trump administration when the president falsely claimed the 2020 election was stolen. Shortly after, DeMaio and other GOP lawmakers introduced unsuccessful bills to tighten voter restrictions before he pivoted to orchestrating a citizen-led ballot initiative last year.

“Recently Trump has promoted the idea that large numbers of undocumented people are voting, for which there isn’t any evidence,” Pitney said. Democrats bankrolling the opposition to Prop. 39 are also a who’s who of California politics.

The state Democratic Party is by far the largest contributor at nearly $5.5 million, followed by the Sonoma-area Federated Indians of Graton Rancheria with $2 million.

Longtime Democratic donors Patty Quillin, a film producer and wife of Netflix CEO Reed Hastings, and Quinn Delaney, a real estate investor and philanthropist, have each pitched in $1.5 million. Labor heavyweights such as the Service Employees International Union have contributed $1 million.

Democratic gubernatorial candidate Xavier Becerra and Democratic Assembly Speaker Robert Rivas have created a joint committee to raise money for the No campaign and U.S. Sen Alex Padilla is stumping at events.

Nearly 90% of Californians now vote by mail, according to the secretary of state’s office . That means the vast majority of voters would be required to write their Social Security or driver’s license number on their ballot should the initiative pass.

Many people aren’t going to be comfortable with that, No on 39 campaign spokesperson Tenoch Flores said. “This is about creating new avenues to reject valid mail ballots,” Flores said.

“Yes on 39” spokesperson Meredith Shields told CalMatters that no one from the campaign could be made available for an interview. DeMaio declined an interview with CalMatters for this story. Uihlein did not respond to phone calls and emails requesting comment.

Megadonor Uihlein and his wife, founders of the Wisconsin-based packaging company Uline, have poured millions into the Restoration of America PAC, a super PAC that frequently bankrolls Republican candidates in Illinois and Wisconsin. The Uihleins have donated $35 million to the PAC this year alone, and Prop. 39 is the latest target in their effort to fund agenda-setting conservative causes.

Shanahan, an attorney and the former wife of Google executive Sergey Brin, has funneled $370,000 into the Yes campaign, while the Winklevoss brothers have each contributed $250,000.

The interest from the ultra-wealthy in Prop. 39 is a sign that the GOP could be looking to replicate a similar playbook in toss-up states, Sonoma State University political science Professor David McCuan said.

Republican proponents want to see how well or poorly voter ID does in Democratic-heavy California. If it does better than expected, that might mean a similar ballot measure could be fairly popular in more moderate battleground states, such as Michigan, Wisconsin or Pennsylvania.

“There is a spillover effect if you do better than expected, even if you lose,” McCuan said.

Several Republican states moved to expand voter restrictions after the 2020 election, including Wyoming, Kentucky and Oklahoma. And while voter sentiment toward Trump is at historic lows, the GOP was surprisingly successful at getting the voter ID measure on the California ballot.

The “Yes on 39” TV campaign has begun airing ads distancing the measure’s supporters from Trump, while the No campaign released an ad airing in the Bay Area featuring images of Trump and characterizations of Prop. 39 as a “power grab.”It’ll likely still be a tough road ahead for the Yes campaign. The default position for most voters is “no” on ballot propositions, meaning supporters of the measure will have to persuade enough voters to agree with them.

An April poll by the UC Berkeley Institute of Governmental Studies showed Californians broadly support requiring voters to present identification at the polls, but it found that support dipped below 50% when respondents were given specific details about the measure, such as that it’s meant to combat alleged voter fraud. A Public Policy Institute of California poll in September found support for Prop. 39 has dropped to 43%.

While this could be effective at turning out liberal voters, it’s unclear how even a hot-button issue will be enough to get Republicans out in a midterm election cycle with an unpopular president.

“It’s hard to pass a red-coded measure in a blue wave election,” Pitney said.

This story was originally published by CalMatters and distributed through a partnership with The Associated Press.