One March night in the nation’s capital, Senator J.D. Vance, Republican of Ohio, left a conservative gala to join a group having dinner with Donald Trump Jr.

As the meal wrapped, Mr. Vance decided, on a whim, to invite a friend, whom he had just introduced at the gala dinner, to meet the former president’s son. Soon, the three Republicans — Mr. Vance, Mr. Trump Jr. and Mr. Vance’s friend, David Sacks, the Silicon Valley entrepreneur — were getting to know one another for a half-hour or so in a private dining room of the Conrad Hotel.

It was there, at that impromptu post-dinner hang hours after Mr. Trump became the presumptive Republican nominee, that Mr. Sacks signaled that he was all-in for Trump 2024.

On Thursday evening, this time on his own California turf, it will be Mr. Sacks’s turn to host Team Trump. The former president himself is flying to San Francisco to attend a fund-raiser at Mr. Sacks’s $20 million home on the toniest street in the city’s tony Pacific Heights neighborhood. The private event, the first campaign fund-raiser since Mr. Trump’s criminal conviction last week, is expected to raise north of $12 million, according to people involved in the gathering.

Beyond the money, the fund-raiser in the beating heart of the liberal tech industry is also shaping up to be a landmark event, at least symbolically.

Four years ago, and certainly eight years ago, the Bay Area remained a haven for liberalism and offered little support for Mr. Trump. But that Obama-era bonhomie between Silicon Valley and the Democratic Party has come close to disintegrating. These days, entrepreneurs complain as much about President Biden as they do about Lina Khan, the chair of the Federal Trade Commission, who has ascended to Darth Vader-like status in some corners of the technology industry.