Fauci and Birx worked together at the dawn of the AIDS crisis. Thirty-seven years later, they are partners in fighting the coronavirus.

After childbirth, she resumed researching the disease under Fauci’s tutelage.

That disease would soon be known as HIV/AIDS. Birx and Fauci have worked together every year since on successful efforts to manage the illness and on a continuing search for a cure and vaccine.

Now, 37 years after they first worked together, the longtime allies often stand at the White House with President Trump to brief the nation about the novel coronavirus, while they privately join forces to try to convince the president that more economically painful measures are needed to stem the outbreak.

In doing so, and in walking a tightrope between their science-driven views and the president’s reliance on gut feelings, they have drawn criticism from the left and the right. The story of how they walk that line is rooted in the way they have relied heavily on each other for decades and on the lessons they learned fighting another disease that initially had no treatment, they both said in separate interviews with The Washington Post.

“No one will understand what it was like to be a fully trained physician at a time when you thought you were relatively knowledgeable and have patients dying and unable to stop it. And unable to know what it was,” said Birx, 64, the U.S. global AIDS coordinator. “And I think that drew both of us to conquering infectious disease . . . because once you had that devastating experience, you don’t want to live that in any epidemic again.”

Fauci, 79, director of the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, or NIH, recalled it similarly.

“We’ve known each other so long, and we’ve been through so much, the good times and the bad times, the successes, the failures,” he said. “So we’re kind of like two veterans that have been through a bunch of wars together.” When they realized they were going to work together advising the White House on how to fight the coronavirus, Fauci said, they told each other: “Well, here we go again, we’re back together again.”

The two doctors and a number of their associates said that even though HIV/AIDS is a very different disease from covid-19, the disease the coronavirus caused, the lessons from their prior work are clear. In both cases, there was early misunderstanding about the seriousness of the illness, the government was slow to react, and the initial response relied on behavioral changes while a longer-term solution was sought.

Now their task is to apply those lessons, but their effort to work alongside Trump has led to some jarring statements, and there were some initial questions about whether they were entirely in sync. Fauci has been both hailed and pilloried for his blunt refutation of some of Trump’s declarations, such as when he told Science magazine, “I can’t jump in front of the microphone and push him down” when the president makes an incorrect statement.

Birx, meanwhile, recently told the Christian Broadcasting Network that the president “has been so attentive to the details and the data,” adding that he has been “attentive to the scientific literature.”

Given Trump’s well-documented aversion to reviewing written briefing materials, her comment was mocked by President Bill Clinton’s former press secretary Joe Lockhart, who derided her on Twitter for having “drunk the Kool Aid” and urged that she tell the truth to Trump about the depth of the crisis.

Birx defended her comments, telling The Post her job as a public servant is to make sure Trump understands the data, and she said he has “asked the right questions.”

By the time Birx and Fauci briefed Trump about what would happen if social distancing guidelines were lifted prematurely, they presented such a unified voice that the president dropped his desire to end restrictions in time for Easter Sunday and agreed with them that at least an additional 30 days was needed.

Birx, according to Fauci, is in a more difficult position because she is a political appointee who can be dismissed at any moment, while he is relatively protected in his role as an administrator in the NIH system. While they both have served presidents of both parties going back to the Reagan administration, he is used to speaking bluntly without fear of reprisal.

“She has to be a little bit more deferential because of the fact that she is a political appointee,” Fauci said. “But when it comes to presenting the science, we’re really like, one unit, there’s no separation between us at all.”

That has been the case since the two met in 1983.

Birx was an Army captain working at Walter Reed Army Medical Center in Washington, D.C., and Fauci worked at the National Institute of Allergy and Infectious Diseases, where he would become director the following year.

After Birx gave birth to her eldest daughter in 1983 and rejected a blood transfusion because of safety concerns, she devoted herself to discovering a treatment for the disease killing so many around her. That work evolved as she served her fellowship in Fauci’s laboratory, and the two then spent several decades working together to find a therapy or cure for HIV/AIDS.

“We were in the middle of it,” Fauci said. “We were both taking care of HIV-infected individuals, me here at NIH, her across town at Walter Reed. And it was dark years for both of us. We were taking care of patients, and they were all dying.”

Birx recalled that she would make rounds at the clinical center at NIH and then return to her post at Walter Reed, where hundreds of soldiers in their 20s and 30s suffered from a little-understood disease.

“You can’t imagine the devastation,” Birx said. “And I think that’s why both of us, when we see what’s happening at the front lines with the health-care workers [caring for coronavirus patients], that’s an experience we have both been in.”

Soldiers in combat

Nelson Michael, who worked with Fauci and Birx at the time, said the bonding experience of watching patients die was “no different than combat veterans” who saw their fellow soldiers killed.

Michael, who now is director of the Center for Infectious Disease Research at the Walter Reed Army Institute of Research, said he told Fauci recently that the fight against the coronavirus reminded him of their battle against HIV in the late 1980s and early 1990s, and he agreed. “For those of us who grew up and fought the HIV war, and are still fighting it quite honestly, this pandemic hits us really hard,” Michael said.

After a decade of research, scientists who received funding from Fauci’s institute discovered that a combination of antiretroviral drugs could be used to manage, but not cure, the disease. “That success changed both our lives at the same time,” Fauci said of himself and Birx. They pivoted to how to help HIV patients around the world and to finding a cure.

Fauci and Birx soon pushed for one of the most difficult challenges in medicine: a vaccine to prevent HIV.

Unlike a vaccine against infections such as the coronavirus, which theoretically can be based on how a person’s immune system fights back, an HIV vaccine would have to work differently and is considered far more difficult. Birx, in her role as the director of the HIV research program at Walter Reed, pushed for a vaccine trial in Thailand, working with that country’s military.

The idea was criticized by some in the scientific community who doubted the test could be successful and thought funds could be better spent on managing the disease. Birx was far short of the needed funding. Then, in 2001, the Pentagon proposed eliminating her budget to fight HIV/AIDS.

Fauci came to the rescue. After meeting with Birx, he helped convince the Pentagon to keep its funding and then pledged his institute’s money to bolster the vaccine budget. It was a defining moment in their relationship, he said.

“When I invested those tens of millions of dollars to support Deb’s trial, people criticized me for that,” Fauci said. “People in the scientific community said, ‘You are wasting money, you shouldn’t be spending money on a trial that may not work.’ But we forged ahead.”

The trial started in Thailand and resulted in an efficacy rate of 31 percent, which Fauci considered “one of the high points” of his partnership with Birx, a modest success that was good enough to lead to larger trials in South Africa.

Birx, after serving as director of the Centers for Disease Control and Prevention’s Division of Global HIV/AIDS, was named in 2014 by President Obama to be the U.S. ambassador on global efforts to combat HIV/AIDS. At her swearing-in ceremony, she praised Obama for “his bold leadership” and lauded her new boss, Secretary of State John F. Kerry, for his “amazing, long-standing and unyielding commitment” to fighting HIV/AIDS. She remains in her ambassadorial role during the Trump administration, making her an Obama holdover.

While she and Fauci spend “every working hour” on science related to infectious diseases, she said, they have often crossed paths personally. She said they both have daughters who participated in the same cross-country meets, and she has seen him “cheering on his daughter like I cheered on mine. I’ve seen him as a father. I’ve seen him as a husband. . . . We’ve shared things on a scientific and a personal level. He’s just been a fixture in my life for the entire time.”

Given their partnership, they have been together on countless panels, including a December 2017 appearance at an AIDS forum at The Washington Post, at which they expressed optimism about the vaccine trials in South Africa. In January, it was announced that one of the trials had failed, but Fauci stressed in the interview that others are continuing and hold promise.

A new battle

It was around that time that the seriousness of the coronavirus was becoming apparent in the United States. In late February, while Birx was attending an AIDS conference in Africa, Vice President Pence named her as White House coronavirus response coordinator. After an overnight flight from Africa, Birx arrived at the White House for a meeting of the virus task force, on which Fauci was already serving in his role as the government’s leading infectious disease specialist.

A key challenge for Fauci and Birx has been to deliver realistic, science-driven assessments of the growing crisis to the public, even as the president sometimes gives conflicting and incorrect statements and espouses his own theories.

Over the past several months, Trump has said the virus “miraculously goes away” by April, that “we have it totally under control” and that anyone who wants a test can get one. A photo of Fauci at one briefing with Trump, in which he puts a hand to a lowered forehead as if in disbelief, has been widely published.

Myron Cohen, who has known Fauci and Birx since the 1980s, said the pair are too driven by science and data to be subject to political pressure.

“They’re scientists, and they’re public health officials,” said Cohen, director of the Institute for Global Health and Infectious Diseases at the University of North Carolina’s Department of Medicine. “They’re not politicians. They lay out the facts. . . . This is a once-in-a-lifetime thing, and these are the right people.”

About a week ago, Fauci and Birx faced their greatest challenge so far in advising the president. Trump had said he wanted to end federal guidance on social distancing by April 12, which the two doctors argued would result in a massive death toll.

They traveled to the White House to persuade Trump to drop his idea.

Birx, the data expert, brought along charts. Fauci, who has excelled in communicating complex ideas in layman’s terms, brought his blunt style and backed Birx.

Fauci and Birx stood in the Oval Office with their charts, leaned over the Resolute Desk and asked Trump to examine the data. The charts showed that if Trump’s idea was pursued, more than 2 million people could die. But if social distancing and stay-at-home policies were followed nationally for 30 days, then there would be 100,000 to 240,000 deaths. “I guess we got to do it,” the president said.

Speaking at a White House briefing on Tuesday, Trump essentially said he had entrusted the nation’s future to what he was told by the pair of doctors, whom he referred to as Tony and Deb. When a reporter asked Trump what he believed the death toll would be if the public followed social distancing restrictions, the president said, “I’d rather them say the numbers.”

As crushing as the virus crisis has been, Fauci said he and Birx are confident this fight is winnable, in part because a vaccine against the coronavirus probably can be developed with known scientific strategies that should pay off within the next 18 months, much faster than their continuing efforts to eradicate HIV/AIDS.

“When you talk about how did the experience that we had back then inform what Deb and I do now, it’s kind of like deja vu all over again,” Fauci said. “Here we are up on the stage in the press room in the White House. Turn back the clock 35 years, and that’s us talking about HIV. So that’s what we mean when we sort of look at each other and sort of say under our breath, ‘Been there, done that.’ ”