(WASHINGTON) — Dianne Feinstein, who became California’s first female senator and went on to serve six terms, the longest of any woman in Senate history — and whose political career was forever changed by the assassination of two colleagues — has died, multiple sources confirm to ABC News. She was 90.

Over her three decades in the Senate, Feinstein transformed from a barrier-breaking member of the Democratic Party’s liberal vanguard, championing the legalization of same-sex marriage and a ban on assault-style weapons, to one of the Washington’s establishment members, esteemed by lawmakers on both sides of the aisle but increasingly criticized by outside progressives who argued that she refused to step aside for the next generation.

In her final years, her work on Capitol Hill had also begun to be overshadowed by concern about her mental and physical health even as she insisted she remained a robust public servant, despite her hospitalizations, reports of episodes of confusion and other issues.

In announcing earlier this year that she planned to retire at the end of her latest term, in 2025, Feinstein said: “Each of us was sent here to solve problems. That’s what I’ve done for the last 30 years, and that’s what I plan to do for the next two years. My thanks to the people of California for allowing me to serve them.”

Journalist Rebecca Traister, who profiled Feinstein at length for New York magazine, told ABC News for this obituary that she believes Feinstein’s approach to politics was less tethered to an absolutist ideology than to defending and supporting the importance of rules and order.

Feinstein’s political positions changed over time, but what didn’t was how she saw her job: “as somebody who was within these institutions to uphold the rules,” Traister said.

She said what she found most surprising about Feinstein was that devotion to the institution — outside of politics.

She cited how, in the early 1960s, before Roe v. Wade, Feinstein determined punishments for abortion providers during her time on a women’s sentencing board, where Feinstein later said she saw “not medical people — these were truly the coat-hanger type of abortions.” As a pro-abortion access supporter in college, Feinstein reportedly helped a woman get to Mexico where abortion was legal, Traister said.

“She believed in civic and political control and order, and I would say that is the defining feature of her life in politics,” Traister said, adding, “Sometimes that led her to positions that were on the left and sometimes it led her to positions that were on the right.”

Feinstein’s early life and path to the Senate

Born Dianne Emiel Goldman in 1933 in San Francisco, the first years of Feinstein’s life were filled with hardship. Jerry Roberts, author of the Feinstein biography “Never Let Them See You Cry,” described Feinstein’s mother, Betty, as an alcoholic who frequently beat her and her two sisters, citing in his book moments where she chased Feinstein with a knife and once nearly drowned one of Feinstein’s sisters in a bathtub.

“Their mother was both emotionally and physically abusive. She [Feinstein] was very much the matriarchal figure in terms of protecting her younger sisters and taking the brunt of things,” Roberts said.

Feinstein’s surgeon father, Leon, was just as instrumental in shaping her. A barrier-breaker himself, he was the first Jewish chair of surgery at the University of California at San Francisco’s medical school.

“She really identified with her father and his kind of propriety and status,” said Traister. “But it’s certainly true that as the oldest sibling in that household, she really developed a passion for how to keep things in line and under control that I think you can see working its way through her political life.”

After serving six years on California women’s sentencing board, Feinstein ran for — and won — a race to be on the San Francisco Board of Supervisors, beginning the first of three terms in 1970.

Her third term as a supervisor was her last and, as she suggested to reporters on the morning of Nov. 27, 1978, it was intended to be her final chapter in politics. She had lost two mayoral bids, was facing health problems and recently lost her second husband to cancer.

Then tragedy struck.

Later that November day, a colleague on the board, Supervisor Dan White, assassinated Mayor George Moscone and Supervisor Harvey Milk, California’s first openly gay elected official.

It was Feinstein who found Milk’s body, subsequently recalling how her fingers slipped through a bullet hole in his body as she went to take his pulse. With TV cameras rolling, she was the one to tell a shocked city about the slayings. As the president of the Board of Supervisors, she became the city’s first female mayor.

“It sounds like it was scripted in a movie. She leans in, tells reporters she’s leaving politics — you can’t make up something like that,” said Los Angeles Times columnist Mark Barabak, who covered Feinstein going back to her San Francisco days.

She went on to win two terms as mayor.

Barabak said Feinstein “held up the city on her shoulders … the city was really on edge.” She was “thrust in the middle of it” and “really rallied and really helped keep the city together,” he said.

As mayor, she enacted a handgun ban and survived a recall attempt over it, foreshadowing a decadeslong fight over the same issue when she served in the Senate.

Her profile grew quickly. She was on Democratic presidential nominee Walter Mondale’s vice presidential short list in 1984. After losing her own race for governor of California in 1990, she successfully ran in a 1992 special election to serve out the remainder of Republican Pete Wilson’s term — becoming the first women elected from the state to serve as a senator.

In Washington

More firsts followed: Feinstein became one of the first two women to join the Senate Judiciary Committee, with the support of then-Chair Joe Biden. She made it her mission to pass a ban on assault-style weapons, telling The Los Angeles Times that Biden was “ultimately supportive but initially skeptical,” fearing that the measure might stymie a broader bill focused on crime. But he nonetheless thought it would be a good “lesson” for her if she wanted to give it a shot.

The opposition was fierce. Idaho Republican Sen. Larry Craig was one of the people who challenged her, saying, “The gentlelady from California needs to become a little bit more familiar with firearms and their deadly characteristics.”

Feinstein replied, “I am quite familiar with firearms. I became mayor as a product of assassination. I found my assassinated colleague and put a finger through a bullet hole trying to get a pulse. I was trained in the shooting of a firearm when I had terrorist attacks, with a bomb in my house, when my husband was dying, when I had windows shot out. Senator, I know something about what firearms can do.”

The ban, which included some exemptions and came with a sunset date of 10 years, to bolster its support, became law in 1994. Feinstein continued to push for similar laws in her remaining time in office.

She was also known for championing same-sex marriage and in 1996 was one of 14 senators who voted against the Defense of Marriage Act — the law, later overturned, that prevented the federal government from recognizing same-sex marriage — nearly two decades before the Supreme Court ruled that same-sex marriage was a constitutional right.

Barbarak said her extensive time in San Francisco likely shaped her ideas on the issue. “The gay community was very large and influential in San Francisco, in a way that really it wasn’t in any other city in the country,” he said. “And that was just part of the political culture. It was just part of being mayor of San Francisco.”

But the accomplishment that she told reporters was the most important work of her career was during her time as chairman of the Senate Intelligence Committee. Feinstein called for a full investigation of the CIA’s detention and interrogation program after Sept. 11.

Because of her push for further transparency under both the Bush and Obama administrations, it was alleged that the CIA repeatedly misled the public and mismanaged the program, which was “far more brutal” than the agency previously had conveyed, with torture ranging from waterboarding prisoners often dozens of times to severe sleep deprivation, including a detainee who was chained to the concrete floor and appeared to die from hypothermia, ABC News reported at the time.

The subsequent, Feinstein-backed report from the committee found the methods used on more than 100 detainees were “not effective.”

Probing the CIA’s tactics was risky for Feinstein, in part because she was challenging her own party. “There was an enormous amount of opposition including from the [Obama] administration to not make this stuff public,” Traister said.

But that doggedness was consistent with “how seriously she took the violation of norms that she so believes in,” Traister said.

“When she discovered that they had been behaving outside of the expectations … it was like hellfire. She really went after them hard,” Traister said.

Annette Bening went on to play Feinstein in the 2019 drama about the CIA probe, “The Report.”

“I just think that’s real legacy stuff, which she did there because nobody wanted that report out … certainly the CIA didn’t,” said Roberts, her biographer. “That was, I think, a demonstration of her independence and her determination and her ability to fight.”

But her independence was often seen in more recent years as too moderate compared to other Democrats, especially as a representative of one of the country’s most reliably blue states.

During the contentious Supreme Court confirming hearings for Brett Kavanaugh, liberal groups criticized Feinstein for hugging Republican Sen. Linsey Graham and praising him for running “one of the best hearings I’ve participated in.” Then-Senate Minority Leader Chuck Schumer later told reporters they had a “long, serious talk” about it.

And the way she dismissed school children who urged her to support the progressive “Green New Deal” to address climate change went viral after she told them, “I’ve been doing this for 30 years. I know what I’m doing. You come in here and you say it has to be my way or the highway. I don’t respond to that … I was elected by almost a million-vote plurality and I know what I’m doing.”

The interaction was satirized on Saturday Night Live.

Final years and service amid decline

In the final years of her political career, some voices in Feinstein’s own party grew louder in saying that she should retire. Her defenders, too, often spoke up for her. In 2017, then-House Speaker Nancy Pelosi called her a “strong voice and a staunch advocate for the people of California.”

During Feinstein’s last and final campaign for Senate, the California Democratic Party backed challenger Kevin de León instead. At the time, León said he was offering “a new voice, a new change represented in California of today, not of the past.”

Feinstein still won by a landslide — by roughly a million votes. But the discontent continued.

In April 2022, Feinstein’s home paper, The San Francisco Chronicle, published a piece citing multiple anonymous staffers and Senate colleagues who said Feinstein’s memory was “rapidly deteriorating. They said it appears she can no longer fulfill her job duties without her staff doing much of the work required to represent the nearly 40 million people of California.”

Feinstein pushed back in an interview with the Chronicle’s editorial board. “I meet regularly with leaders. I’m not isolated. I see people. My attendance is good. I put in the hours,” she said then, echoing what she told The Los Angeles Times in 2020: “I don’t feel my cognitive abilities have diminished. … Do I forget something sometimes? Quite possibly.”

In February 2023, Feinstein announced she would not be seeking reelection, telling reporters soon after, “The time has come.”

Schumer said during a closed-door lunch meeting when she made her announcement, “She got a standing ovation that lasted minutes and minutes and minutes. One of the longest I’ve ever seen, which shows the love that our caucus and our country have for this wonderful, wonderful leader and legend.”

Feinstein’s pending retirement was soon eclipsed by her health struggles. For three months in 2023, she remained at home in California to recuperate from shingles, which also caused her to suffer brain inflammation and Ramsay Hunt syndrome, which affects facial nerves.

That absence also temporarily halted Democrats’ ability to confirm nominees through the Judiciary Committee on which Feinstein sat.

California congressman Ro Khanna and some others called for her to step down. But she never left her job.

That tenacity, Barabak said, fueled her success as much as the controversy at the end of her career.

“She’s very determined. She’s very stubborn. She’s very dogged,” he said, adding, “She’s shown, time and again and again and again, [she] is not someone who is going to be pushed around. I think that this is pretty consistent with who she has been her whole career, her whole public life.”

ABC News’ Benjamin Siegel contributed to this report.

This is a developing story. Please check back for updates.

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