Three decades of service in the US Senate came to an abrupt end this morning for the woman who touched off power plays and controversy over incapacity. Dianne Feinstein, the oldest member of the upper chamber, passed away overnight at age 90. She leaves behind a grieving family and a big political hot potato for Democrat leadership:

Sen. Dianne Feinstein, D-Calif., a vocal advocate of gun-control measures who was known for trying to find common ground with Republicans during her three decades in the Senate, has died, according to two sources familiar the matter. She was 90.

Feinstein, the oldest member of the Senate, the longest-serving female senator and the longest-serving senator from California, announced in February that she planned to retire at the end of her term. She had faced calls for her resignation over concerns about her health. …

Thrice married, Feinstein was predeceased by her husband, investment banker Richard Blum, who died last year. She is survived by her daughter, Katherine Feinstein, a San Francisco County Superior Court judge; her son-in-law, Rick Mariano; and her granddaughter, Eileen Feinstein Mariano.

First off, now that Feinstein has gone to her rest, our prayers are with her and her surviving family. Regardless of politics and other disputes, she served in the Senate and the nation. This has to be a crushing blow to her family, who must have hoped that she would have some time left to spend with them in retirement.

Now, of course, the problem of her succession becomes completely acute for Gavin Newsom and Democrats, and not just those in California. Feinstein’s apparent incapacity had already touched off a contentious primary fight even before she announced her retirement at the end of this term. That primary has drawn several House Democrats into a fight for the seat, including Adam Schiff, Barbara Lee, Katie Porter, and other state-level Democrats. There’s also a question about whether Nancy Pelosi’s daughter, who became a Feinstein aide and some speculated her caretaker, might want to pursue the seat.

Had Feinstein survived to the end of her term, Newsom would have been left off the hook in determining Feinstein’s successor. The primary process would have allowed him to avoid the infighting, at least until the general election, where California’s open primary system would likely have produced two Democrats as the final candidates.

Now, however, Newsom has no choice but to intervene and appoint a temporary replacement. Democrats only had a 51/49 majority in the Senate with Feinstein, and that relied on three independents and Joe Manchin to continue caucusing with them. Newsom made black voters and women angry when he appointed Alex Padilla to replace Kamala Harris in 2021 and believe Newsom owes them an appointment of a black woman next. Barbara Lee certainly thinks so, and she will get very vocal about that, likely immediately. Pelosi reportedly wants Schiff, Karen Bass may want a piece of this debate, and term-limited governor Newsom may want to think about taking on the job himself.

The problem for Newsom is that choosing anyone practically ends the primary process. The only way to avoid that — and if Newsom wants to run for president, he probably needs to avoid it — is to appoint someone without any ambition in this electoral cycle, and especially to avoid any of the already declared candidates. The smartest choice might be Nancy Pelosi herself, as long as she’s ready to retire from her House seat. That would allow her to go out with another historic resumé item and keep the primary process undisturbed. Failing that, he could ask Barbara Boxer to return for the next sixteen months. (I know, I know …)

Newsom has nothing but bad choices ahead of him here. I suspect he’s tempted to appoint himself and claim he’s not going to stick around, but don’t be surprised if he talks himself into a full Senate run if Biden refuses to retire. All that campaigning has to pay off with something.