In 1984, when Anthony Fauci took over as head of the National Institute of Allergy and Infectious Diseases (NIAID), his wife gave him a plant for the new office. Both the palm and the 81-year-old physician are still there, the giant plant now crowding the office of one of the most celebrated—and polarizing—scientific figures in U.S. history. But not for much longer. Fauci announced on 22 August that he would step down at the end of the year from both NIAID and his post as the chief medical adviser to President Joe Biden.

“What am I going to do with this plant? It’s a monster. I can’t fit it in any other place,” he joked this week from his NIAID office to Science‘s senior correspondent Jon Cohen, who has conducted many candid interviews with the institute chief, starting more than 30 years ago with the emergence of an earlier pandemic, AIDS.

For many people in the United States, Fauci became the public figure trusted above all others to guide them through COVID-19. The hero worship was evident in Fauci bobbleheads, “In Fauci We Trust” yard signs, and baseball cards that feature him throwing out a first pitch. But many others—including former President Donald Trump and some of his top advisers—turned on Fauci. They saw his advice as inconsistent and misleading, and portrayed him as a threat to the social order, the economy, and the health of the public. In this alternative world, the yard signs say “Fauci for Prison,” T-shirts declare “Even My Dog Hates Fauci,” and ballcaps call him a fraud or worse. He and his family have faced death threats, and his house has had a Secret Service detail stationed outside for protection.

In a 2021 webcast interview at the annual meeting of AAAS (the publisher of Science), Fauci said he wouldn’t retire until there were vaccines for HIV, malaria, and tuberculosis (TB). In his interview with Science this week, Fauci explained his change of mind, acknowledged some missteps during the pandemic, and discussed what he might do next. The interview has been edited for brevity and clarity.

Q: What triggered your decision to leave at the end of this year? You had a much longer range view when we spoke in February 2021 for the AAAS meeting, and then you later said you would retire at the end of Biden’s first term.

A: No, no, I never said that I would retire at the end of Biden’s first term. Please go back and look at my words. Somebody asked me on television, If Donald Trump was the next president, would you stay and work with him? And I said, it doesn’t matter if he’s the next president or if there’s another Republican or even if Joe Biden has a second term. I don’t plan to be here at the end of the day.

I walked onto the National Institutes of Health (NIH) campus as a 27-year-old guy who just finished his medical residency at the New York hospital, and it’s 6 decades years later. I’ve accumulated an unprecedented amount of experience. One of the things I had wanted to do deep down was to be here at the end of the discovery of an HIV vaccine. And this is the truth–and I’m telling you and I haven’t told anybody—I said, you know, we’re not going to get an HIV vaccine for another decade at least. I was joking when I said malaria and TB.

Q: You really haven’t answered the question precisely. Was it the threats to your three daughters and your wife? The attacks in the media and Congress? What is it that finally just made you say, I’m done with this job?

A: It was none of the above. As a guy whose known me for decades, I don’t lie to you. As the Trump administration was ending, I was vaguely considering wanting to have at least a few years when I’m still energetic, enthusiastic, and passionate about doing something outside of the realm of the government. Then the president calls me up right after being elected and says, One of the first things I’m going to do, Tony, is ask you to be my chief medical adviser. I said yes, fully thinking that at the end of that first year of the Biden administration, we’d be done with COVID, it really would be in the rearview mirror.

At the end of that year, it became clear that that’s not going to happen. And I had long conversations with my best adviser, namely my wife, who said, you know, this is not going to disappear. [Fauci’s wife, Christine Grady, heads the bioethics division at NIH’s Clinical Center.] So I said to myself, you know, I’m going to be 82 in December, what do I have further to offer?

Despite the knives and the slings and the arrows, I’ve achieved a degree of being kind of a hero to some people. So let me use that to inspire people. So I said, when can I do that? I decided over the spring and summer that the best time to do it is when you’re getting somewhat of a steady state with this disease, so I could transition out of here.

Q: Is some of the vitriol toward you about being a flip-flopper with your pandemic advice a result of having to make public health decisions in public in real time?

A: When you’re doing an experiment, you collect data, you validate it, you scrub it, you analyze it, and then you write something that’s based on science that’s not dynamic, but is immutable. When you’re dealing with a pandemic response, it’s very dynamic, and a somewhat mysterious evolution of a process that has a lot of consequences, because people’s lives are involved. The public expects you to analyze the situation and come out with daily proclamations about what should be done. When you’re humble and scientific enough to say, You know, we were saying this a week, a month, 2 months ago, but now things have really changed, that’s taken as flip-flopping, being wrong, and having made a mistake.

The classic one I know that you’re referring to is about masks, right? How many times are we gonna go over that? The surgeon general tweets, Please do not buy masks, the Centers for Disease Control and Prevention says, Masks are unnecessary. I, as one spokesman, say, You know, we don’t know if it works outside of the health care setting. Nobody is fully aware of the aerosol spread. And we had no real idea that 60% of the transmissions were by an asymptomatic person. So, right then, we shouldn’t necessarily be wearing a mask. As soon as [the known facts] changed. I said, Whoa, wait a minute, we better be wearing a mask in an indoor setting. And that becomes flip-flopping arrogance.

Q: In retrospect, do you think you could have framed it more cautiously in the early days and said, We don’t really know enough right now, it doesn’t look like we need masks, and there’s a shortage of N95s?

A: Yeah, probably so but that’s not what people want to hear. They want to hear what should we do? I probably should have retrospectively couched it in a way that was a little bit more flexible. But I can tell you, Jon, if I did, it’s likely I would have been labeled as a wallflower, he didn’t know what he was talking about.

Q: So what are you going to do? You’ve said you’re going to write a memoir. You’ve never been much motivated by money.

A: If I was motivated by money, I would have taken the 100 jobs I’ve been offered for 20 times my salary.

I don’t know, Jon, and I’m being very honest with you. Let me tell you what I did. I went to the Office of the General Counsel, and I said, I want to know what I can plan [for my post-NIAID retirement]. And they said, if you want to stay pristine, you plan nothing until you walk out the door. Then no one can accuse you of any conflicts of interest, of letting out little signals about what I’m going to do. Why are you looking so skeptically at me?

Q: I just imagine you have some dreams.

A: I don’t know what that’s going to be. It may be hooking up with a university that’s willing to make me a senior professor on their faculty. It may be going with a foundation. I can tell you one thing I’m not going to do. I’m not going to sit in my house with a Gmail address.

Q: You’ve published more than 1100 papers. Your first one was in 1965 on celiac disease, and then over the next 15 years, you published 62 papers on Wegener’s granulomatosis. That could have been your career. You never broke into Nature or Science with those papers. It isn’t until AIDS surfaced that you started regularly publishing in high-impact journals. You were already well into your career before you found what became your deep passion and focus.

A: When I started seeing desperately ill young gay men, it turned me around. That moved me like I never was moved before in medicine. And I decided I was going to pivot. I had had a very successful career that had already gotten me into most of the societies, the young Turks, the old Turks, but then I said, this is really something that I want to devote my career to. From the fall of 1981, right up through the time that we had very successful antiviral drugs, I was taking care of very, very sick people who had HIV. And that inspired me with a passion that we really have got to learn about this disease. And that’s what got me being fanatically a workaholic, about research on that.

Q: Looking back, who was the easiest president to work with? I know who the most difficult one was.

A: I wouldn’t want to say who was the easiest. They were very different. And the difference often was dictated by the circumstances that defined their presidency. I had a very, very warm, almost grandfather-to-grandson relationship with George H.W. Bush. A fine, fine, gentlemen. I had probably the most impactful relationship with George W. Bush, because he allowed me to be the chief architect of the President’s Emergency Plan for AIDS Relief (PEPFAR). If you want to look at my career, in lives saved, the most important thing I’ve done might be PEPFAR. [PEPFAR has invested $100 billion in helping more than 50 countries prevent and treat HIV infections.] But I wouldn’t have been in a position to do what I did with PEPFAR unless I had the president trusting me as I did in [Bill] Clinton’s administration.

Q: Do you think NIH directors should stay in the same position for decades, the way you have? Or should NIH set term limits?

A: It should be flexible. And it depends on the individual and on what’s going on. I don’t buy those kinds of broad statements. I think you should be evaluated the way we are, every 4 years, by an outside group. I’m all for performance-based longevity.

Q: Do you have any advice for NIH about who they should look for or what type of person?

A: The type of person but not a person—that would not be appropriate. You need somebody who clearly has scientific credibility and really understands the science. It also has to be somebody who is articulate enough to be able to navigate the degree of public exposure you will have, because you will be involved in the next outbreak and the next public health crisis, which very often is an infectious disease.

Q: What do you want to accomplish between now and December?

A: I’d like to guide the good research being done in the arena of both mucosal, nasal vaccines for respiratory diseases, as well as more durable vaccines that protect against entire families of viruses. I’m a pusher. We meet as a group at least three, four times a week and I go OK, what are we doing? I try to be not a pain in the ass, but I’d like to keep my foot on the pedal between now and then to keep that thing going.

Q: I’ve seen loads of people confront you over more than 30 years. No one seems to get under your skin as much as Senator Rand Paul. Why does that guy piss you off so much? [The Kentucky Republican has accused Fauci of helping to trigger the pandemic by funding scientists in Wuhan, China, whom Paul and others allege either created SARS-CoV-2 or had an accidental lab leak of a bat virus they had collected.]

A: I came into what I thought was a good faith, oversight hearing where politicians ask questions for the purpose of improving the situation, for the purpose of protecting and preserving the health of the country. When you start off by saying, How do you explain the fact that you are responsible for the death of 5 million people? No way am I going to stand for that on public television, on C-SPAN. Sorry, Jon. No way.

Q: You got into a debate with him about the meaning of gain of function. [The Wuhan scientists combined a bat coronavirus growing in culture with a piece from another one, and the chimeric virus, in mouse experiments, was more deadly than the original one—but it could not have been used to create SARS-CoV-2.]. The Tony Fauci I know, who’s very calm under pressure, would have said, yes, the virus in this experiment gained some function, but that’s not what we’re talking about here. We’re talking about whether it met a definition of gain and function that put the public at risk.

A: You’re absolutely right. If I had to do it over again, I would have done it a little differently. Instead of responding to his accusatory tone, I should have just said, That’s irrelevant to the safety of the country. It stunned me when he publicly called me a murderer of 5 million people. I just should have dropped back off and said, This guy’s a jerk.

There’s an important difference between that kind of attack versus when the AIDS activists were attacking me in the ’80s. What they were saying was based on real suffering, reaching out to get my attention. So when they put my head on a spike outside this window, those were people who were hurting, and they wanted me to listen to them. And I did listen to them. And it was one of the best things that I’ve ever done. I never, ever got angry with the activists.

Q: If the House of Representatives becomes Republican-majority, and they hold hearings, will you testify?

A: If I’m asked to testify, I’ll testify. I have nothing to hide. I can explain everything I’ve done and I could defend everything I’ve done. But if it becomes clear that it’s not an in-good-faith oversight, but a character assassination, I might not play ball.

Q: A last question for you. Do you have a motto that you told your kids, like, this is what I learned in life?

A: Yeah, it’s what I go by. It’s called precision of thought and economy of expression. Know what your message is, know your audience, and say it in as few words as possible.