When Sen. Dianne Feinstein, D-Calif., returned to the Capitol this month, a beaming Senate Majority Leader Charles E. Schumer was waiting for her as the gray sedan zoomed up, while a crowd of reporters and photographers looked on.

Feinstein, 89, looked frail, and part of her face appeared to droop, which her office would disclose more than a week later was caused by a separate condition triggered by the shingles that had sidelined her since February. Aides helped her into a wheelchair and then quickly pushed her inside to the Senate floor, where Feinstein quietly said "aye" and cast her vote - the moment her colleagues had been waiting months for.

Feinstein's allies say that she has been doing her job since returning more than a week ago - casting votes that are needed to boost Democrats' narrow majority in the Senate and approving President Biden's judicial picks. But the shock of seeing Feinstein's visibly weakened state - paired with her apparent confusion in some interactions with reporters - has created rising alarm that is rippling across both Washington and California about her fitness to serve. At the same time, there is no consensus about what should be done - and virtually no visibility into her thinking about how she will manage her duties over the next year and a half as she continues to rely on an insular circle of aides, revealing very little to the public.

The standstill around the issue has been intensified by the competing interests of the three Democratic members of the House from California who are vying to replace Feinstein in the 2024 election: Adam B. Schiff, Katie Porter and Barbara Lee. All of them are allied with powerful leaders in the party who would have the ear of California Gov. Gavin Newsom (D) were he forced to appoint a replacement for Feinstein if she stepped down before the end of her term.

There were fresh questions this past week about whether Feinstein had been transparent with her constituents when it was disclosed that her case of shingles had triggered encephalitis, an inflammation of the brain, as well as Ramsay Hunt syndrome, which causes facial paralysis. (A spokesperson said the encephalitis had resolved but "she continues to have complications from Ramsay Hunt syndrome.") Before those complications were confirmed by her spokesman - only after they were reported in the New York Times - her office had not detailed any information about her medical condition beyond the shingles diagnosis and had declined requests to provide information from her doctors.

Amar Shergill, chair of the Progressive Caucus of the California Democratic Party, said there is concern that the public has not gotten the full picture about the medical complications Feinstein was experiencing before she returned to Washington and alarm that she has struggled "during simple conversations with reporters about when she was working and when she wasn't."

"Democrats are now wondering whether she's actually capable of representing her constituents in D.C.," said Shergill, who has endorsed Lee in the race to replace Feinstein. "This is a very important time with the impending default and the budget, and we need a senator who is involved in those discussions, and advocating in the press and taking meetings. It seems very clear that she's not going to be able to do any of that."

But there is also no evidence of a groundswell of California groups or activists demanding that Feinstein step aside - beyond the coalition of 60 liberal grass-roots groups that urged her to resign last month. It is widely known in California Democratic circles that the senator built a career premised on her refusal to bow to pressure, with former aides and colleagues noting that the harder Feinstein is pushed, the more determined she becomes to keep her own counsel.

"The pressure isn't the thing that's going to get her to act. It's going to have to be a realization that she and her senior people will have to make about how sustainable this is given her abilities or lack thereof," said California Democratic consultant Roger Salazar. "I just don't see her leaving under anything but her own terms."

Susie Tompkins Buell, a top Democratic donor in California who admires Feinstein, said she believes many people aren't speaking up about their concerns about her health because she seems so vulnerable and they want to be respectful. This past week, Buell told the Times she thinks Schumer or Newsom have a responsibility to do something.

"I think everyone is torn between their compassion and scratching their head about practically, what they can do about this," Buell told The Washington Post.

A Feinstein spokesperson declined to comment for this article but pointed to a previous statement in which the senator said: "I'm back in Washington, voting and attending committee meetings while I recover from complications related to a shingles diagnosis. I continue to work and get results for California."

There is no indication that either Schumer or Newsom think it is their role to urge Feinstein to step aside, particularly in the midst of the contentious three-way Democratic race to replace her.

Upon Feinstein's return to the narrowly divided Senate, Schumer, who spoke to her on the phone several times during her absence, said she is "exactly where she wants to be." Her presence solves difficult math problems for him and the White House when Sen. Joe Manchin III (D-W.Va.) and other vulnerable Democrats up for reelection decide not to back Biden nominees.

Newsom, who has known Feinstein since his earliest days in politics, would have the responsibility of appointing Feinstein's successor if she were to leave office early - which could become one of the most consequential and politically fraught decisions he has had to make.

The Democratic governor, widely viewed as a future White House contender, was under intense pressure to appoint a Black woman to the Senate when Kamala D. Harris vacated her seat to become Biden's running mate, because her departure meant that there were no Black women serving in the chamber.

Instead, he chose then-Secretary of State Alex Padilla, who became the first Latino senator from California. Newsom subsequently promised during an MSNBC interview that he would choose a Black woman if he were given another chance to make a Senate appointment.

When Newsom made that promise in 2021, two natural choices were near the top of his list: then-Rep. Karen Bass, who is now mayor of Los Angeles, and Lee, who was not yet a candidate for Senate.

"At that time it was just a throwaway line on cable TV to satisfy a disgruntled constituency," said Dan Schnur, who teaches politics and communications at the University of California at Berkeley and at the University of Southern California and Pepperdine University. "Now he's trapped by it. If he does not appoint Lee, if he does not appoint a Black woman - he angers the African American community. If he does appoint Barbara Lee, he enrages a lot of very powerful supporters of the other candidates."

While some have suggested that Newsom could choose a Black woman to fill a "caretaker" role through the end of Feinstein's term - to avoid putting his thumb on the scale for any of the three Democrats running for the seat - several of the prominent Black female politicians who would naturally be candidates for that role have said they are not interested. And Newsom could face a backlash for overlooking Lee given that she is the longest-tenured of three candidates, the highest-ranking Black woman appointed to Democratic leadership in the House and a past chair of the Congressional Black Caucus.

Aimee Allison, who founded She the People, a national network aimed at elevating the political power of women of color, noted that she was involved with the statewide network of women calling for Newsom to appoint a Black woman in 2021.

Allison, who is backing Lee in the Senate race, said that although Newsom appointed Padilla, "he responded to that call publicly by making that commitment and promise, and we took him at his word."

"Many of us, including myself, find the conversation about caretaking unacceptable," Allison added. "There was never a conversation about a caretaking role when it came to Senator Padilla. Why is there an exception for a Black woman?"

Back in Washington, Feinstein's return to the Senate has been unsteady. She has attended multiple Judiciary Committee hearings, and on Thursday, she briefly praised law enforcement as the committee passed legislation in honor of National Police Week.

"There was no program more favorable with people than police on the streets," she said of her tenure as mayor of San Francisco. "They got to know them, there was a positive relationship, the crime rate went down, and I came away from the job really understanding the necessary for the juncture."

The senior California senator has also taken a handful of questions from reporters as she's been guided to votes, occasionally sounding confused. "No, I haven't been gone," she told a reporter from the Los Angeles Times who asked about her colleagues' reaction to having her back in the Senate, appearing irritated. "No, I've been here. I've been voting."

On another day, she incorrectly denied that she had suffered encephalitis during her bout of shingles, telling a CNN reporter that she had just had a "bad flu." (Her office later clarified that Feinstein "misspoke" because her doctor had not used the medical terminology with her when describing her complications.)

Sen. Richard J. DurbinD, -Ill., the chair of the Judiciary Committee, told reporters this past week that he could not be the judge of whether she was fit to serve and that his staff were "monitoring" her health condition on a daily basis to ensure that she could be present for votes.

"She has to make that decision for herself and her family as to going forward, but we're happy to have her back," he said.

Critics have argued that her family and friends should persuade her to resign. And former senator Claire McCaskill, D-Mo., who said she considers Feinstein a friend, took to Twitter to say Feinstein's "legacy is being tarnished" by her return to the Senate with such serious health issues. But Feinstein's allies say that the senator herself pushed to return and that calls for her resignation have not deterred her.

Former California governor Jerry Brown defended Feinstein in an interview with CNN on Friday, arguing that she was forced to return to the Senate because it's unclear whether Republicans would allow a new senator to be seated on the Judiciary Committee even if she resigned. Republicans blocked Schumer's request to temporarily replace her in April.

"There's a real challenge here that [is] exacerbated by the Republican policies," Brown said. "Feinstein has what it takes to participate over the next several months."

It's unclear how real that threat is, however. Committee assignments are almost universally uncontroversial measures that happen at the start of a Congress, when senators unanimously approve both Republican and Democratic assignments by a voice vote. But if someone does object to a senator's committee assignment, that placement then needs 60 votes to be approved.

Republicans argued that the earlier request was unprecedented, given that no senator appears to have been "temporarily" replaced on a committee in recent memory, and that it was even more unusual because Feinstein wanted to keep her other committee assignments. Some Republicans, including Sens. John Thune, R-S.D., and Thom Tillis, R-N.C., said at the time that if Feinstein were replaced by a new senator, that would be a different situation and suggested it would not draw the same opposition. Democrats would probably need nine Republicans to agree to seating the new member.

"There's a huge difference between temporarily replacing a member on one of her committees for the sole purpose of advancing partisan judicial nominees and refusing to permanently sit an entirely new member on all committees," said one Republican Senate aide, who spoke on the condition of anonymity to disclose internal conversations.

And despite the heightened scrutiny of her performance, Feinstein has faced no public pressure from Senate colleagues to resign.

"We're all human and we all have health issues, and right now she is performing as a United States senator doing her job," Sen. Richard Blumenthal (D-Conn.) told reporters this past week.

The Washington Post's Marianne LeVine contributed to this report.