Schiff fired the first salvo last month by openly admitting his long-known interest in the seat, telling a Los Angeles television station that, after his House leadership bid fizzled, he would “consider running for the Senate if Senator Feinstein decides not to run for reelection.” Schiff also met with Feinstein to inform her of his intentions, according to two people familiar with the exchange.

Feinstein’s plans remain a wildcard. The 89-year-old senator’s standing has eroded as California Democrats sour on her centrism and the San Francisco Chronicle detailed her perceived cognitive decline in an explosive piece this spring that bolstered previous reporting by POLITICO about Feinstein’s capacity to serve.

But while it is widely believed that the California senator will not seek another term in 2024, she has not said anything explicit about her intentions — a Feinstein spokesperson contacted about the story said he had “no updates” — and people who know her say she bridles at being backed into a corner. Californians eyeing Feinstein’s seat have been careful to show respect for the longest-serving woman in U.S. Senate history and have, for the most part, avoided overt positioning.

But the détente is unlikely to hold for much longer.

“Just by virtue of the calendar and her age, the playbook is getting to a climax here,” said a prominent California Democratic bundler who requested anonymity to discuss a sensitive campaign matter. “People who have interest have been talking to people about their interest.”

Schiff is one of multiple California House Democrats who could seek the seat. Porter, fresh off beating back a Republican challenger in one of the state’s most competitive races, is “absolutely considering a 2024 Senate campaign” as she hears from admirers around the state, according to a person close to Porter.

And Khanna is being urged to run by progressives aligned with Sen. Bernie Sanders, whose presidential campaign Khanna co-chaired. Lee plans to spend the holidays discussing her plans with her family, according to a source familiar with her intentions.

All of those possible candidates would bring assets to the race. And under California’s top-two primary system, it’s likely a U.S. Senate race would yield two Democrats squaring off in the general election, as happened when Kamala Harris defeated then-Rep. Loretta Sanchez in 2016.

Both Schiff and Porter are formidable fundraisers, although Porter’s competitive House contest drained much of her resources. Schiff achieved national stature as a fierce antagonist of former President Donald Trump and for his role in impeachment proceedings. Porter quickly became a star for her acerbic and whiteboard-assisted grilling of executives.

Lee has long been seen as a top contender to win an appointment if Feinstein resigns. California Gov. Gavin Newsom vetted Lee when he was seeking a replacement for former California Sen. Kamala Harris, who is Black and Asian American, and later committed to choosing a Black woman if he gets to make another Senate appointment. The longtime Oakland congresswoman is widely respected in the Bay Area and could marshal deep Black support.

And Khanna is beloved by progressives and could divert rivers of money from his affluent Silicon Valley district.

The next few months could determine the field. Contenders will be working to secure endorsements and fundraising commitments — and to freeze out their foes in the process.

“Anyone who is sophisticated enough to think about running for one of California’s two seats in the U.S. Senate is fully aware of the dynamics, and dynamics include the option of getting out early, staking your claim, and discouraging challengers,” said Darry Sragow, a Democratic former political consultant and publisher of the election analyst California Target Book.

But it’s unlikely that anyone will have the field to themselves. California’s overwhelmingly Democratic electorate makes a U.S. Senate seat close to a lifetime position. Even if the race doesn’t affect the balance of power in the Senate, it’s certain to be a multimillion-dollar melee.

“This isn’t something you do at the last minute. It takes tremendous preparation, and tremendous organization and messaging and money and all of those things,” Boxer said. “Anyone who’s interested in this, with full respect to Sen. Feinstein, should start securing the support they need.”