With no statewide officeholders, little pull in the Legislature and a dwindling number of registered voters, California Republicans have teetered on the brink of irrelevancy for years.

But there’s an unlikely savior on the horizon who could help them inch back toward relevancy just in time for the June 7 California primary: Donald Trump.

The Republican presidential campaign front-runner is projected to be very close to securing the 1,237 delegates for the GOP nomination on California primary day, and analysts predict his name on the ballot could bring 15 to 30 percent more Republicans to the polls — both to vote for and against him. Only registered Republicans can vote in the party’s closed GOP primary, where 172 delegates are up for grabs.

The immediate beneficiaries of a Trump bump could be the Republicans on the U.S. Senate ballot, none of whom has been given much chance to finish in the top two in the race and advance to the general election in November. Bolstered by their party’s wide advantage in registered voters, two Democrats — Attorney General Kamala Harris and Rep. Loretta Sanchez of Santa Ana, have led in polls and raised millions of dollars. Their GOP rivals — former California Republican Party Chairmen Tom Del Beccaro and Duf Sundheim — are miles behind in both the polls and cash raised. Wealthy Silicon Valley businessman Ron Unz, a 1994 GOP candidate for governor and the author of 1998’s Prop 227, which effectively eliminated bilingual education in California, also entered the race this month.

Heavy GOP turnout forecast

Typically, about 46 percent of the voters in a California primary vote Republican. But the Trump factor — and the love-him-or-hate-him voters he is expected to drive to the polls here, as he has elsewhere — could boost Republican turnout enough to vault one of the Republicans into the top two.

“Frankly, I had written that race off as having the two Democrats in the top slots until this week” when the California primary became relevant because of Trump’s delegate math, said Jennifer Duffy, a senior editor at the nonpartisan Cook Political Report who analyzes Senate races nationally. “I think Republicans are now in a position to at least take a shot at one of those (top two) slots. A shot.”

It’s only been a few days since more definitive predictions of California’s relevancy started surfacing after Tuesday’s primary contests in five states scrambled the delegate math. So it is a bit early to find tangible signs of a Trump bump. Sacramento political consultant Paul Mitchell has not noticed an uptick in Republican voter registration.

“If (a surge) does materialize, it would impact down-ticket races,” said Mitchell, vice president of Political Data and one of the state’s leading experts on California’s racial and demographic groups. Mitchell has promised to run around the state Capitol naked if two Democrats advance to the general election in the Senate race.

Speculation over impact

So far, in the five primaries where there have been Senate races on the ballot, “Trump voters are not taking their anger out on other Republican candidates,” Cook’s Duffy said. “I don’t see a Trump voter going in and voting for anybody but a Republican.”

Other analysts, candidates and campaign insiders say that while they’re forecasting more GOP voters, they just don’t know which voters will show up. Not even the candidates are sure.

“I don’t know if you can draw a straight line from (Trump) to people voting for our campaign,” Del Beccaro said.

Sundheim, nevertheless, has felt the Trump bump. He hired a fundraiser last week for his bootstrap campaign, “and I couldn’t have done that before. There’s definitely more excitement now.” A California supporter of Sen. Marco Rubio of Florida, who suspended his presidential campaign last week, offered to connect Sundheim with 1,000 volunteers who were planning on campaigning for Rubio.

Sundheim, who thinks the GOP turnout could bounce by 50 percent, is noticing a difference when he gives his campaign business card to people.

“I’ve been handing those things out for six months,” Sundheim said. “Now they want to stop and talk with me.”

The conventional wisdom is that if Republican turnout increases, it could bump Sanchez, currently second to Harris in polls, from the general election. But Sanchez campaign adviser Bill Carrick — a veteran California consultant who has advised Sen. Dianne Feinstein — thinks turnout might increase only to 30 percent.

“At the beginning of the cycle, I thought it might be 25 percent turnout,” Carrick said. “I don’t think (the increased turnout) will affect the Senate race all that much, especially now that you have three Republicans splitting their vote.”

Middle-of-road voters

Former South Bay Rep. Tom Campbell, who has run several statewide races in California, thinks Trump will bring out more middle-of-the road voters.

“The more conservative voters are going to turn out anyways,” said Campbell, who supports Ohio Gov. John Kasich, whom he knew when they served together in the House. “This might bring out more moderate voters, and that helps Kasich.”

In California House races, the Trump-juiced primary could boost Republicans seeking to make the general election to replace Rep. Lois Capps, a Democrat who is not seeking re-election to her coastal San Luis Obispo-centered district seat, said David Wasserman, who analyzes congressional races for the Cook Political Report.

“Otherwise, I don’t see it affecting other House races yet,” said Wasserman, who believes GOP turnout in California could increase by 30 percent in June.

Good news for Bay Area

But Ted Costa, the godfather of the 2003 California recall — one of the last big Republican-led political earthquakes — doesn’t believe Trump’s presence will change the Senate race.

“I don’t believe in coattails for anyone. Not even Trump,” said Costa, who is volunteering to help the Trump campaign find delegates in California. Nonetheless, Costa predicts that Trump will get 55 percent of the GOP primary vote — the same amount former Gov. Arnold Schwarzenegger took in his 2006 re-election.

The bad news for the presidential campaigns about the sudden relevancy of California’s primary is that now they have to quickly pull together operations in the nation’s largest state. The good news for Bay Area residents is that because Republicans allot three delegates for each congressional district a candidate wins the popular vote in, voters who live in super-liberal San Francisco or Oakland will see a Republican presidential candidate in their midst for the first time since the Pleistocene Epoch. Three delegates earned from San Francisco count just as much as three delegates earned from GOP-heavy Kern County.

Texas Sen. Ted Cruz’s campaign is far ahead organizationally in California, having secured supporters across the state months ago. They’re going to be strong in the more conservative Central Valley and among evangelical voters there and in the Inland Empire of Riverside and San Bernardino counties.

Cruz devotee in Mission

Kasich’s operation — whose top adviser in California is former state Insurance Commissioner Steve Poizner — will probably target a dozen or so congressional districts along California’s more liberal coast. Trump doesn’t have much of an operation in the state, but that’s been his modus operandi most everywhere so far, and it’s been working.

In another sign of an unpredictable campaign season, one of the most devout Cruz volunteers lives in San Francisco’s Mission District — which is better known as a warm bosom of support for liberal Democratic Sen. Bernie Sanders.

But there in his apartment, Tom Canaday volunteers 60 hours a week for the Cruz campaign, mostly harvesting supporters on social media and connecting them to the campaign. After selling his gourmet pork business, he had some extra time while he looked for his next venture. He’s an evangelical Christian and fiscal conservative who found Cruz to be the most thoughtful candidate in the race.

“We’ve had this funny situation that we’ve been building this campaign for months — and didn’t know if there would ever be a meaningful campaign in California,” Canaday said. “Now the future is here. It’s clear that it will be meaningful.”

Joe Garofoli is The San Francisco Chronicle’s senior political writer. Email: jgarofoli@sfchronicle.com Twitter: @joegarofoli