She stands before television cameras just hours after the news breaks that the U.S. government has been conducting a massive surveillance program, compiling a database of Americans’ phone records and monitoring foreign terrorism suspects’ Internet traffic.

Her hands form fists.

“It’s called protecting America,” says Dianne Feinstein.

A five-term California Democrat who chairs the Senate intelligence committee, Feinstein hardly needs to flex her muscles these days to command deference. On Sunday talk shows and from podiums around the Capitol, she’s playing the role of chief congressional defender of the surveillance program to skeptical colleagues and critics who say it’s Big Brother run amok. She is also one of the most senior members of the powerful Judiciary and Appropriations panels.

Just as she is playing such high-profile roles, Feinstein, who turned 80 on Saturday, is blazing a new political trail as a symbol — an unwilling one — of the changing workplace.

“It’s a non-role as far as I’m concerned,” Feinstein says. “I’ve always had the belief that age is just chronology. I know people who are 50 who are older than I am.”

With the death of Sen. Frank R. Lautenberg (D-N.J.) this month, Feinstein became the Senate’s oldest member, a distinction never before held by a woman. In fact, there’s only been one other female senator over 80: Rebecca L. Felton, an 87-year-old, lace-collared white-supremacist suffragette who was appointed to a vacant seat from Georgia and served for less than two months in 1922.

Feinstein’s age is in most ways incidental to her success; in others, it’s key. She’s benefiting from the privileges that seniority brings in the Senate and from a work ethic forged in an era where women had to work twice as hard as their male counterparts to succeed.

There are now a record 20 female senators, many of whom have taken on high-ranking roles such as chairmanships of key committees that can help ensure long political life spans. They may soon be as likely as men to grow old in elected office — or in any office.

Women over 60 make up the fastest-growing segment of the workforce, notes Elizabeth Fideler, a fellow at the Sloan Center on Aging and Work at Boston College and the author of “Women Still at Work: Professionals Over 60 and on the Job.” And the sight of older woman at the office — even when that office is the Capitol — is becoming more familiar. “Obviously, politics is a bit harsher an arena, but people are willing to accept an older person so long as they remain effective,” she says.

Age is a sensitive topic for anyone. For politicians, even more so. When Sen. Bob Dole (R-Kan.) at 72 launched his presidential campaign in 1995, Time magazine’s cover asked, “Is Dole Too Old for the Job?” And recall Sen. John McCain’s (R-Ariz.) anger at a question about his age during the 2008 presidential campaign. (McCain was 70, and called the questioner a “little jerk.”)

If the politician in question happens to be a woman, she’s even more likely to get The Question or be the target of late-night vitriol.

In 2007, at the age of 67, Nancy Pelosi (D-Calif.) became speaker of the House — the highest-ranking woman in the history of the republic — and a feast for comedians’ Botox jokes.

“Nancy Pelosi said today we’ve waited 200 years for this,” Jay Leno cracked after Pelosi was sworn in. “Two hundred years? How many face-lifts has this woman had?”

Former congresswoman Pat Schroeder (D-Colo.) predicts that even as women remain in office into old age, the public will never tolerate “a female Strom Thurmond,” a reference to the late South Carolina Republican senator who left office at the age of 100, his final years spent with staffers and colleagues overlooking (and compensating for) his diminished mental and physical powers.

“The public would turn on her,” Schroeder says. “Not like they did with Strom, who everyone thought was funny — this kind of character.”

Tall and unstooped, Feinstein is often seen striding down the Capitol’s marble halls.

Even her political adversaries say she remains more engaged in the minutiae of her job than many of her younger counterparts.

“I always think if I’m half as prepared and energetic as Senator Feinstein, I’m doing okay,” says Sen. Claire McCaskill. The Missouri Democrat calls Feinstein “the ideal of what a senator should be.”

“Role model” is the one part of her new status that Feinstein embraces. “That is the biggest compliment,” she says.

Former secretary of state Madeleine Albright says the scrutiny that female politicians will draw in their older years will be just a continuation of what they have faced at other points in their careers. “They’ll talk about [Feinstein’s] hair — but that’s what happens now anyway,” she says.

It did, at least, early in Feinstein’s career, when media reports swooned over her looks and her impeccable ensembles. “Charm Is Only Half Her Story,” was the headline of a Time magazine 1990 story, which described her as “a casting director’s idea of a Bryn Mawr president who must be bodily restrained from adding gloves — or perhaps even a pillbox hat — to her already ultra-conservative banker-blue suits and fitted red blazers and pearls.”

Ask friends and colleagues to describe Feinstein and something surprising happens.

“She does her homework,” says former senator Olympia Snowe (R-Maine).

“She does her homework,” says Sen. Saxby Chambliss (R-Ga.), the vice chairman of the intelligence committee.

“She just does her homework,” says Sen. Barbara Boxer (D-Calif.)

At home, as in the office, Feinstein works constantly. That includes spending her days off poring over thick briefing books and, always, the “weeklies,” a stack of the memos she requires every member of her staff to submit each Friday.

In the memo, each employee — from top policy advisers to mailroom clerks — describes what he or she has done that week: meetings they attended, people they met with, legislation they worked on, or what kind of letters have been coming in from constituents. Feinstein scours them, and then asks pointed questions at mandatory Monday-morning staff meetings in her Washington office.

This interrogative style has led some former staffers to grouse that she is a tough boss, prone to calling out underlings, even in group settings where such queries can come off as insults. Mark Kadesh, a lobbyist who was her longtime chief of staff, says that the rigors of working for her weren’t for everyone. “The thing is that she’s no more demanding of herself than she is of her staff,” he says. “If you couldn’t keep up, it was tough. If you accepted that challenge, it was a great experience.”

Yet colleagues — even Republicans — find her approachable. “You knew that she always came to her conclusions based on real knowledge and understanding, not in a partisan way,” Snowe says.

Chambliss credits her with helping to smooth over the once-strained relationship between the Senate and House intelligence committees. The bipartisan leaders now meet regularly to talk about how to speak with one voice on tricky issues — a change from the past. “We couldn’t afford that — the world has become too dangerous a place on intelligence issues,” he says.

Feinstein’s always-be-prepared ethos seems, in part, a holdover from an earlier time. When she first entered public office as a member of the San Francisco Board of Supervisors in 1969, few women held elected offices. Those who did faced far more scrutiny than their male counterparts.

Feinstein recalls being the top vote-getter in her first election to the board, which by law, meant she would be its president. But some, citing her inexperience, called on her to cede that position to the second-place man. She politely declined. Her ascent from supervisor to mayor was accompanied by tests. “You would get pressed,” she says. “And so you learn to know your stuff.”

To this day, Feinstein enters no forum— be it a hearing with top military brass or a one-on-one with a low-level staffer — without excruciatingly detailed preparation.

“On the NSA issue, none of the members had gone to these briefings, and yet they’re all talking about them — whereas if Dianne hadn’t gone to them, known everything about them, she’d have the grace not to say something,” Schroeder says. “My jaw always drops when I see someone who’d rather be at the gym or running to the airport who wants to stand up and criticize something they don’t know anything about.”

While she’s surely come a long way from those board meetings in San Francisco, the tests still come.

In March, Feinstein had a YouTube-able moment when she spoke before the Senate Judiciary Committee about her proposal to ban assault weapons. Sen. Ted Cruz, a Republican freshman from Texas and a tea party favorite, prefaced a question to her with a discourse on the Constitution, in which he informed Feinstein (who has served on Judiciary for 20 years and was the panel’s first female member), that the Second Amendment gives people the right to bear arms.

“I am not a sixth grader,” she replied, calmly, but with a rare edge to her voice that indicated that she was just a bit peeved with the gentleman from Texas. “It’s fine you want to lecture me on the Constitution. I appreciate it. Just know I’ve been here for a long time.”

And may be longer still. Feinstein, who won reelection in 2012, will be 85 when her term ends. Will she run again? “Ask me in three years,” she says.