Marc Benioff, the chief executive of Salesforce, drew national attention in 2015 when he said he would move his employees out of Indiana if a new state law that would have legalized discrimination was not changed. (It was.)

But predictions that, for better or worse, tech and politics were henceforth going to be inseparable did not hold up.

Tech got political, fast. Sergey Brin, a Google co-founder born in Russia, told 2,000 employees who were demonstrating against Mr. Trump's actions in January 2017 that "some of us might even adopt Pence 2017 bumper stickers." It was all but a direct endorsement of the new president's impeachment.

What is happening — or rather not happening — in San Francisco is part of a broader urge in the tech community to stay behind the scenes in state and national politics. The overwhelmingly Democratic-leaning Silicon Valley was shocked by the 2016 election of Donald J. Trump and aghast at his anti-immigration ban, which cut to the heart of their existence as a multinational industry whose companies have often been founded by immigrants.

That is quite a contrast to the last open mayoral election, in 2011. Tech leaders were featured in a video for their preferred candidate, Ed Lee, who went on to win and was re-elected in 2015. It has been viewed more than 600,000 times on YouTube. This year, several candidates are vying to replace Mr. Lee, who died in December , but none of them has tried to enlist tech in anything so striking.

But as voters go to the polls Tuesday to choose a mayor in one of San Francisco's most disputed elections in recent memory, the industry that set off a high-rise construction boom and has been blamed for a housing crisis in the city is fading into the background.

Over the last decade, this has become the tech industry's hometown.

Mr. Benioff, a native of San Francisco and the most prominent tech executive in the city, was a financial backer of Mr. Lee. But he said in an interview Friday that the mayoral election was too important, too closely fought and too contentious for him to support any of the top four candidates: Jane Kim, Mark Leno, Angela Alioto or London Breed.

"This is the hottest election San Francisco has ever had for mayor," he said. "I care so deeply, I cannot support one of the candidates. I don't want to disenfranchise my ability to work with whoever is elected."

Sam Altman, the president of the influential start-up accelerator Y Combinator, has not tweeted about politics all year — surprising reticence for someone who flirted with the idea of running for California governor last year.

"I've just been super busy," Mr. Altman wrote in an email, adding that he had "no idea" why others had been so quiet. A spokesman for Reid Hoffman, the LinkedIn co-founder who previously showed an intense interest in politics, waved off an inquiry, saying: "Don't really have anything new to report."

Mr. Brin has no political thoughts to share at present, a Google spokeswoman said. Even Peter Thiel, who backed Mr. Trump when hardly anyone else in Silicon Valley would, appears not to be making any donations at the moment.

Hunter Walk, formerly with Google's YouTube and now a venture capitalist, appeared in the 2011 video supporting Mr. Lee. "That was the beginning — and end — of my viral video career," he said. Others in the video were Marissa Mayer, then chief executive of Yahoo, and Biz Stone, a co-founder of Twitter.

Mr. Walk said he was supporting Ms. Breed, the mayoral candidate who seems to have the most backing from tech. Mr. Stone said he was "usually not public about politics" but had been helping Ms. Breed "with social media strategy and expertise," introducing her to knowledgeable people. Ms. Mayer, who could not be reached for comment, gave $500, the legal maximum, to Ms. Breed.

If tech is determined to be low key about San Francisco politics, there is an eminently practical reason: fears of a backlash.

Ron Conway, a venture capitalist, was widely regarded — and sometimes condemned — as the power behind the throne for Mr. Lee, whose reign was very good for tech. Attempts to hold Uber and Airbnb responsible for skirting regulations largely failed. Twitter got a major tax break to stay in the city.

Mr. Conway championed Ms. Breed, a president of the board of supervisors who became interim mayor after Mr. Lee's death, as the next mayor. At Mr. Lee's funeral, he told Mr. Benioff, "We have to focus on getting London elected." (Mr. Conway disputed that, writing, "At most, I acknowledged the historic significance of an African-American woman succeeding the city's first Chinese-American mayor.")

The venture capitalist moved too aggressively, however. The progressive wing of the board of supervisors removed Ms. Breed from the interim position after a few weeks, saying they did not want her to have an undue advantage in the election.

One of the supervisors, Hillary Ronen, said in a direct attack on Mr. Conway that there were "white, rich men — billionaires — in this city"who "steered the policies" of the two previous mayoral administrations. "They got us into this absolute mess we are in today where poor people and people of color cannot afford to live in this city," she said.

Mr. Benioff called Mr. Conway "the Koch brothers of San Francisco," a reference to the siblings who are heavy backers of conservative causes. He added: "That is his prerogative as a citizen of the United States. He feels he's doing the right thing. He's a good person. But he doesn't speak for me or tech."

Mr. Conway now says he has more important places to spend his time and resources than the mayor's race.

"The future of our country and our progressive values are threatened by this president and this Congress, and candidly stopping them is ultimately far more important to me than who is elected Mayor of San Francisco on June 5th," he wrote in an email.

Mr. Conway emphasized that he is still backing Ms. Breed, citing his belief that "she's the only candidate who will truly tackle our city's housing and homeless crises."