Its foes have been relentless, and it now faces some of the most withering attacks of its history. A bill in Congress would strip the organization of federal family-planning grants and a series of covertly taped videos seek to depict some Planned Parenthood staff as willing to assist sex traffickers.
On one side, there are prominent conservatives suggesting that Planned Parenthood may be a criminal enterprise.
On the other, Planned Parenthood leaders and allies are seizing the moment to rally support, saying the ultimate target of the attacks is the ability of American women to get the reproductive health services they desire.
"We've been here for the past 95 years, and we'll be here for the next 95," said Planned Parenthood's president, Cecile Richards.
Through its affiliates, Planned Parenthood operates more than 800 clinics and health centers across the country, serving more than 3 million patients a year.
A half-dozen of those clinics - in New Jersey, New York and Virginia - figure in the undercover videos released over the past two weeks by Live Action, a California-based anti-abortion group. The videos show a man posing as a pimp and a woman posing as a prostitute seeking health services for underage sex workers.
Planned Parenthood fired one clinic manager in New Jersey who offered advice to the visitors, but otherwise says its staff responded professionally and reported the visits to their superiors.
Planned Parenthood's national office notified the FBI before any videos were released and accused Live Action of resorting to deceptive "dirty tricks." It also announced a nationwide retraining program to ensure that clinic staffers were familiar with rules about reporting possible danger to minors.
While much about the videos is in dispute, they provided fresh ammunition for anti-abortion activists promoting a bill introduced by Rep. Mike Pence, R-Ind., that would deny federal family-planning funds to any organization that performs abortions. Pence makes clear that Planned Parenthood is his target; it would lose more than $70 million in annual funding.
"Every American should be shocked that an employee of the largest recipient of federal funds under Title X has been recorded aiding and abetting underage sex trafficking," Pence said. "The time to deny any and all funding to Planned Parenthood is now."
By law, federal funds may not be used directly for abortions. But Pence argues that the grants, by covering overhead and operational costs, free up other money to provide abortions.
Planned Parenthood's staunchest allies in Congress - primarily liberal Democrats - have vowed to fight the proposed funding cut.
"In my community, Planned Parenthood is a very highly regarded mainstream organization," said Rep. Lois Capps, D-Calif., who depicted Pence's bill as "driven by an extreme ideological agenda."
Richards said Planned Parenthood, with a $1 billion annual budget, could survive the loss of the federal grants but would be forced to close some clinics and serve fewer people.
"This would roll back decades of progress for women's health care," she said in a telephone interview.
Planned Parenthood dates its beginnings to 1916 when Margaret Sanger, her sister and a friend opened America's first birth control clinic in Brooklyn. At the time, women couldn't vote or divorce abusive husbands, and contraception was illegal.
The clinic was raided, and Sanger was convicted of disseminating birth control information. Undaunted, she founded two organizations that later merged to form the Planned Parenthood Federation of America.
Sanger's personal legacy is complicated. She opposed abortion - yet the organization she founded now provides a quarter of America's 1.2 million annual abortions. Her views on eugenics and racial issues remain a subject of bitter debate to this day.
Over the decades, Planned Parenthood played pivotal roles in easing laws against contraception, popularizing the birth control pill and setting the stage for the Supreme Court's 1973 Roe v. Wade ruling that established a woman's right to have an abortion.
Its clinics have been repeated targets of bombings, arson and protests. A receptionist at one of its clinics in Brookline, Mass., was shot dead in 1994 by John Salvi, who described himself as a militant foe of abortion.
Abortions account for only a small fraction of the services provided by Planned Parenthood - mainly providing contraception, screening for cancer and testing for sexually transmitted diseases. Many of the clients are low-income women with few other options for non-emergency health care.
At many clinics, demand is high. On a recent workday, the waiting room at the Brooklyn health center, which occupies an entire floor of an office building, was filled to overflowing, and center director Nellie Santiago-Rivera said her 35-member staff often sees 150 patients a day.
Most of the Brooklyn clients are black and Hispanic women in their 20s, many without a primary-care doctor of their own.
"This is their community health center," said Evelyn Intondi, a Planned Parenthood nurse-midwife.
Intondi said the undercover videos had been the topic of much discussion among clinic staff.
"You're angry, you're upset," she said. "You wonder, what's the perception of our clients coming in?"
However, she said the campaigns against Planned Parenthood reinforced her resolve.
"It reignites the fire in your belly that brought you to this in the beginning," Intondi said. "This is what I do. There are definitely some people who don't like it."
Planned Parenthood's foes are active on the federal, state and local level. On Thursday, Virginia's House of Delegates voted to prohibit not only state government but also local governments from allocating money to Planned Parenthood clinics.
The bill's sponsor, Delegate Robert Marshall, objects to the clinics' role in providing abortion but also holds Planned Parenthood responsible for broader phenomena he links to the sexual revolution - including out-of-wedlock pregnancies, adolescent sex and sexually transmitted diseases.
"Clearly this group has been on the cutting edge of attacking moral standards," Marshall said in an interview. "Now we're reaping their revolution, and people are having second thoughts."
While Planned Parenthood says it retains broad public support, some of its critics believe the tide of opinion is running against it.
Melinda Delahoyde is executive director of Care Net, a nationwide network of centers that counsel women with unintended pregnancies on alternatives to abortion. She said the cumulative effect of the undercover videos, public unease about abortion and parental concerns about sex education are taking a toll on Planned Parenthood.
"There are cracks in the dike that are widening on many different fronts," Delahoyde said.
Planned Parenthood leaders say their attitude toward sexuality is a key reason for the animosity they face.
"We are a safe place where people can go and ask difficult questions about sex," Richards said. "We do this for teens and adults, gays and straights, and that really irritates some people who believe sex is only for procreation."
Serene Jones, president of Union Theological Seminary and an expert on gender issues, said Planned Parenthood deserved credit for directly addressing the complexities of human sexuality.
"It would be wonderful if we lived in a world where we didn't need Planned Parenthood, where women had all the information and resources they needed regarding their own sexual health," she said. "But given we don't have that, it fills a very important role."