California Sen. Dianne Feinstein, the longest-serving woman in the US Senate and a vocal advocate for gun control measures, died Thursday night. She was 90.

Her death brings to an end a messy, long-running chapter of national politics centered on her age and health as stories and concerns spread over the last year about her perceived mental decline. The longtime Democratic senator announced in February of this year that she would not be running for another Senate term after frustrating members of her party, constituents, and the press for remaining quiet about that decision for most of 2022 and the first weeks of 2023.

She would have faced a primary challenge had she not announced her decision to retire at the end of her term. A host of moderate and progressive candidates had already begun to float their electoral challenges and gather support while Feinstein was peppered with questions about her future. Two of those challengers, Rep. Katie Porter (D-CA) and Rep. Adam Schiff (D-CA), even launched their campaigns before Feinstein went public with her retirement news. A third, Rep. Barbara Lee (D-CA), announced her bid after Feinstein’s decision.

Those three still have five months before California’s primary day, when voters will decide which two candidates move on to a likely Democrat-versus-Democrat general election contest. But for now, there’s an opening in the Senate that California Gov. Gavin Newsom will need to fill — and he will face intense pressure over his decision.

Feinstein had planned to step away from the Senate

Underlying a lot of Democratic frustration in California and in the Senate were the many issues Feinstein’s deteriorating health and advanced age caused for normal Senate operations — excluding how those contributed to the idea of American gerontocracy.

After announcing that she would be retiring at the end of her current term, Feinstein left the capital for the Bay Area to recover from health complications due to a case of shingles. She remained away from the Capitol for two months — stymieing Senate Democrats’ agenda to confirm judicial nominations in the Judiciary Committee and putting the Senate Democratic majority at risk. Those limits, and Senate Republicans’ unwillingness to let Democrats replace Feinstein on the Judiciary Committee, led to calls for her resignation — demands that she ignored.

Feinstein eventually returned to the Senate in mid-May. She used a wheelchair at the Capitol and appeared to have partial facial paralysis. Her continuing health challenges created new conversation about ableism on the Hill as speculation increased about whether she could do her job, and why she wouldn’t retire early.

Feinstein’s death may complicate the California Senate race

California is one of 38 states that gives their governors the authority to fill vacant Senate seats with an appointment, and this power was used recently: California Gov. Gavin Newsom tapped the state’s secretary of state, Alex Padilla, in December 2020 to fill the seat that Kamala Harris would resign to serve as vice president — partially due to Feinstein’s backing.

Feinstein’s huge influence in the state (Padilla used to work for her, she mentored Newsom, and was good friends with former Speaker of the House Nancy Pelosi) largely forced California Democratic leaders to remain quiet about how that appointment process would work. Still, Newsom had promised after Padilla’s appointment that he would name a Black woman to fill Feinstein’s seat, should she vacate it early.

There’s also an intense primary underway to fill Feinstein’s seat, in which Newsom’s promise has come up again and again: most recently, Newsom has said he won’t choose anyone currently running to fill the seat, telling NBC’s Meet the Press in September, “It would be completely unfair to the Democrats that have worked their tail off. That primary is just a matter of months away. I don’t want to tip the balance of that.”

Ahead of Feinstein’s death, Newsom had reiterated that he hadn’t changed his thinking on the issue. The Senate currently has zero Black women, and only two Black members.

But Barbara Lee quickly criticized Newsom’s remarks on Meet the Press, writing on X (formerly Twitter), “I am troubled by the governor’s remarks. The idea that a Black woman should be appointed only as a caretaker to simply check a box is insulting to countless Black women across this country who have carried the Democratic Party to victory election after election.”

She went on to say that if Newsom does indeed appoint a Black woman, he should install “the best possible person for that job,” seeming to imply that she was that person.

The governor, though, has made it clear Lee won’t be his pick, which potentially means selecting one of the state’s two highest-ranking Black female elected officials: Shirley Weber, who won a full term as secretary of state after replacing Padilla, or state controller Malia Cohen, who beat back a closer than expected Republican challenge last year. One other name that’s been floated is Los Angeles Mayor Karen Bass. However, she’s considered unlikely, as she just won her job during the intense 2022 midterms.

Whoever he chooses could decide to enter the primary themselves, in effort to keep the seat they’d been awarded; if they were to do so, they’d have an incumbency advantage the current lawmakers in the race might find hard to overcome. Or they could become a surrogate and endorse one of the current chief contenders, giving a boost to Porter or Lee, who are both within striking distance of the current leader of the pack, Schiff.

That would seriously shake up the race. At this point, we don’t have a lot of great data, but what we do have paints a picture of a race where no one is dominating. Porter and Schiff tend to poll within a few percentage points of each other, with Lee consistently coming in third place.

Before he launched his Senate campaign in late January, Schiff had the biggest war chest, with about $20 million in the bank compared to Porter’s $7 million and Lee’s $50,000 at the end of last year. By the end of the second quarter of 2023, Schiff and Porter reported huge numbers: Schiff had raised $8.2 million, for a total of $29.8 million of cash on hand, while Porter had raised $3.1 million, leaving her with $10.3 million available. Lee raised $1 million, for a total of $1.4 million.

“If you include all the finances, it reinforces what most people have observed and assumed going in: Adam Schiff is clearly the frontrunner, but not a prohibitive one,” Dan Schnur, a professor at UC Berkeley’s Institute of Governmental Studies and another longtime California political adviser, told me after the first-quarter results — which closely mirrored those of the second quarter — were released. “He’s got a tremendous fundraising base, mostly from his own career, but also from the support he’s gotten from the congressional delegation.”

While Schiff does have an advantage now, he doesn’t have the sort of firm grasp on his primary that former President Donald Trump does in the GOP. And that means the emergence of a new figure, temporary or not, could alter the dynamics of the race.

How Californians will pick their next long-term senator

To further complicate matters, the timeline for appointing a temporary successor for Feinstein isn’t clear. Politico reported Friday that staff at the California secretary of state’s office are still figuring out what kind of timeline state law requires for Newsom to appoint a successor or hold a special election to fill the seat.

And politically, Newsom really doesn’t have much time. The Democratic Senate majority is now one safe Democratic vote smaller, and with a government shutdown looming, Democrats may need every vote they can get. The governor took five weeks to make his appointment of Padilla public. This time, he’ll likely want to move more quickly.

California also recently changed the laws governing temporary Senate appointments and special elections to be compliant with the 17th Amendment of the Constitution. State law now requires that a special primary and general election be held to fill an empty Senate seat for the time between the statewide general election soonest after the vacancy has occurred and the start of the next congressional term (in this case, the time between the November 2024 election and the start of the new Congress in 2025).

That would look something like this:

• Newsom chooses a temporary replacement. They can serve until the next general election is decided, in November 2024.
• A special election has to be held to finish Feinstein’s term, which ends in January 2025. That election has to have its own primary and general election, but it can happen at the same time, on the same ballot, as the ongoing Senate primary and general election. (Newsom can also hold an earlier special election, if more practical.)
• In March 2024, the primary date, voters choose a candidate to fill the remaining time of Feinstein’s term, and a candidate to hold a normal, six-year term.
• In November 2024, the general election date, voters do that again.

Whoever wins the special election serves until January 2025. If that candidate also wins the general election, the candidate serves a full term on top of that until January 2031.

Update, September 29, 2:55 pm ET: This story was originally published earlier on September 29 and has been updated to include new information about how Feinstein’s replacement will be chosen.