SAN FRANCISCO — Silicon Valley's tech titans know they are an ATM for the Democratic Party's politicians. They're just not sure if Bernie Sanders knows it, too.

While Hillary Clinton makes Northern California a regular stop in her incessant dash for cash, her challenger isn't even trying to woo the Valley's wealthy, liberal magnates. Sanders has visited the region just once since launching his campaign, and not to raise money, while Clinton has made three fundraising trips here. And his team is doing little to reach potential donors, even the progressives among them, according to Democratic fundraisers.

"He's done nothing out here, they haven't asked me to host any events, unlike Senate candidates," said Guy Saperstein, a San Francisco lawyer and part owner of the Oakland Athletics baseball team. Saperstein gave Sanders the maximum legal contribution of $2,700 after helping bankroll the unsuccessful movement to draft Elizabeth Warren — even promising her up to $1 million if she did run.

"I get [Clinton] invitations all the time. Obviously, I don't go," he added, noting that he even pledged six-figures to a pro-Joe Biden effort and up to $500,000 if the vice president chose Warren as his running mate.

Sanders' refusal to engage in big money politics provides a striking contrast to Clinton. Northern California trails only Washington and New York, and arguably Southern California, as a campaign cash target for her campaign. And its huge financial role was underscored last week by a 900-person, hour-and-a-half gathering headlined by Clinton at a manor deep in Silicon Valley on Wednesday afternoon and a 290-person event at a Napa winery on Thursday evening.

Meanwhile, the Vermonter's lack of interest in the region's cash is a phenomenon that jibes with his campaign's singular focus on Iowa and New Hampshire this fall. But by not sending emissaries — and not even stopping by the San Francisco area for one of his signature megarallies — the insurgent Vermont senator is missing out on potentially millions of dollars.

"I heard nothing from him or his people" before or after he announced his campaign, said another top Silicon Valley fundraiser who aligned with Obama in 2008 and eventually joined the Clinton team. Some pockets of Northern California would be natural ideological fits for Sanders, the fundraiser mused — if only he took the time to court them.

The Vermonter's lack of a presence in Silicon Valley doesn't stem from ignorance of the region's increasing importance to the Democratic money machine; his pollster, Ben Tulchin, is based in San Francisco. Instead, his team is calculating that Sanders' time is better spent elsewhere.

"When we sat down to develop a fundraising strategy, we thought that if we were going to pursue a traditional fundraising strategy, we weren't going to be able to compete," explained Sanders' chief strategist, Tad Devine, justifying the candidate's absence from the go-to donor circles here. "But our online fundraising has been one of the most successful parts of the campaign."

Sanders' camp has said that it's received more than 1 million contributions, largely over the Internet, and the bulk of them come from small donations like those that come through the website and online services like ActBlue. Clinton's team said 93 percent of her third-quarter donations came in increments of less than $100, but the vast majority of her money comes from substantially larger donations.

While Sanders' campaign leaders briefly debated whether to duke it out with Clinton over San Francisco-area donors, their decision to forfeit the territory reflects both Clinton's institutional strength in the region and a determination that fundraising in the Bay Area would force Sanders to sit down for traditional campaign cash events.

"Bernie Sanders just doesn't do that, whether it's West Coast, New York, Florida, Seattle, Texas, Chicago. Any of the places where Democrats raise significant money individually," added another top Sanders strategist. "Our campaign is done on contributors doing 30 bucks a pop. So we just don't do it."

That's not to say that Sanders is a nonentity in the region: His quarterly fundraising filings show nontrivial support from rank-and-file tech workers in the area, and he even has backing from Apple co-founder Steve Wozniak. He's also visited Southern California multiple times, and he held one of his biggest rallies in Los Angeles. An October Field poll even showed him trailing Clinton by just 9 points in the state.

But it's his apparent absence of interest in engaging the San Francisco area's politically influential and financially powerful Democratic contributors and strategists that's making some party donors wonder how he plans to fund a long-term campaign. While he raised nearly as much as Clinton did in the third quarter overall, she also has a network of allied super PACs supporting her bid including Priorities USA, which had raised $40 million through mid-September.

"No, you don't hear any talk about his campaign here in the fundraising circles, ever," said a second top Obama donor in the area who regularly hosts campaign cash events for Democrats up and down the ballot, but who has received no outreach from Team Sanders, and is now with Clinton.

Neither Clinton nor Sanders is particularly tech-focused, acknowledged a handful of Democratic insiders in the region, but many noted that Sanders has done less outreach to potential area contributors than even Biden's team while the vice president was mulling a White House bid this fall.

Still, the Sanders campaign downplays the importance of such Silicon Valley contributors to its effort, which is focused at the moment on ensuring the senator can compete in Iowa and New Hampshire, the two states that act as a gateway to his longer-term viability. Without having to court donors for an outside group, advisers say, there is little incentive for the Sanders machine to set up an extensive operation in-state — particularly since the California primary itself isn't until June, unlike 2008, when it fell on Super Tuesday.

"We've really developed a strategy that's based on the calendar of primaries and caucuses," Devine said. "We believe California could be a great place for Bernie and potentially a big state to win in the primary process, but I don't see us getting there unless we're looking for media venues, or those kinds of venues, until much later in the process."

That position couldn't be further from Clinton's.

While much of the community has yet to truly tune into the election, the former secretary of state's team proactively wooed Obama's 2008 supporters who did not back Clinton then, and the campaign's finance staff was quick to lock in the backing of some high-level fundraisers who still haven't heard from Sanders despite keeping their Clinton allegiances largely silent, a handful told POLITICO.

Meanwhile, Clinton's campaign has regularly been sending top staffers, including campaign chairman John Podesta and finance director Dennis Cheng, to California regularly. Even campaign manager Robby Mook was in Los Angeles last week, shortly before he'll be hosting a series of conference calls with the campaign's maxed-out supporters.

That group has had to fight to expand the area's donor pool beyond the pre-existing Democratic networks, observed several California fundraisers, but there is little sense of urgency without much competition for Silicon Valley support.

"She planted a flag right from the beginning of the campaign — SF was her third fundraising event of the entire campaign — and has been working the various elements since the spring," explained Chris Lehane, Airbnb's head of global policy and public affairs and a San Francisco Democratic strategist who has helped the Clinton campaign's fundraising operation. But, he added, "This is not 2008, when there was an all-out battle to win the hearts and minds of the tech community."