As the Aids crisis accelerated in the 1980s, Donald Trump, then building his brand as a boldface name in the New York City tabloids, reacted with paranoia, ruthlessness and bigotry.

When his bosom friend and mentor Roy Cohn contracted the virus, Trump “dropped him like a hot potato”, Cohn’s secretary has said. Trump told dinner guests that following Cohn’s final visit to his Mar-a-Lago resort, “I had to spend a fortune to fumigate all the dishes and silverware”. The Associated Press reported in 1991 that Trump “asks women to take an Aids test at his doctor’s office before he wines and dines them”.

Over the same decade, in Bethesda, Maryland, grappling with the HIV epidemic became the life’s work of a fellow New York native, Dr Anthony Fauci. Fauci was one of the first scientists to document “severe opportunistic infections among apparently previously healthy homosexual men”. His lab at the National Institute of Allergy and Infectious Diseases (NIAID) led the charge for a cure, and he became the public face of the government’s fight to stop the virus.

In the intervening 30 years, Fauci has continued his life’s work, leading the effort to contain infectious diseases from Sars to Ebola to swine flu. Trump, meanwhile, has gone from playboy to TV star to US president.

That last extraordinary leap, and the rise in the last four months of the deadly Covid-19 pandemic, has now created a most unlikely and delicate partnership between Trump and Fauci on which the future of the country hinges. The two men appear to share little by way of philosophy, but each night they share a stage in front of a scared nation in the grip of a terrifying pandemic; a nation looking to these two very different men to save it from further disaster.

For Fauci, 79, facing down this coronavirus is a date with destiny he has been working his entire life toward. For Trump, 73, the coronavirus is a rare brush with accountability, a moment when boasts and threats and lies do not work.

To achieve success according to their respective definitions of the word, the two men need each other. Trump needs Fauci to shore up fading public trust in his administration’s disaster response. Fauci needs Trump to take action that saves lives.

Their purposes have been mostly – though not always – well aligned. But the rise of an anti-Fauci movement on the political right – and the president’s frequent intolerance for being overshadowed – have fueled concerns that for all its practical necessity, and the stakes for the nation, the Fauci-Trump partnership could come to pieces.

If that happens, said Derek Hodel, a senior program adviser at Physicians for Human Rights who worked with Fauci as an Aids activist and advocate in the 1990s, it would be a rare defeat for Fauci’s political skills.

“Tony was just a master at relationships,” Hodel said. “This is his sixth administration, and although the dynamics of the Trump administration are louder and crazier than any other administration, they’re not all of them different.”

After graduating at the top of his class from Cornell medical school in the Vietnam war era, Fauci fulfilled a public health service requirement by taking a researcher post at NIAID, where he became director in 1984. He would spend the next five decades there, surfacing in the public eye whenever the country was confronted with the specter of bio-terror (anthrax) or deadly contagion (Ebola).

Working with the current president, Fauci appears to sense that keeping his job depends on keeping Trump happy. When he has contradicted Trump, he has usually done so gently.

When Trump pushed the lupus drug hydroxychloroquine as a miracle cure, Fauci said: “In terms of science, I don’t think we can definitively say it works.” Asked by Science magazine why he did not rebut Trump’s overblown claims about the efficacy of a ban on foreign travelers from China, Fauci said: “Let’s get real, what do you want me to do? … I can’t jump in front of the microphone and push him down.”

The White House last week dismissed questions about tension between Trump and Fauci as “media chatter” and said: “President Trump is not firing Dr Fauci.”

But the drumbeat of calls for Fauci to be ousted have been promoted most aggressively by pro-Trump zealots in the far-right media ecosystem – political bomb-throwers, medical quacks and an unknown number of foreign bots posing as American internet users.

The critics blame Fauci and his fellow scientists for the economic misery tied to the government’s social distancing recommendations – omitting any calculation of what economic and human disaster would result if the viral floodgates were opened.

There are indications that the online mob is gaining traction with the president and other elected officials – and with the American public. Last week, Trump retweeted one Fauci critic with the hashtag #FireFauci.

The voices are growing louder. The Republican congressman Andy Biggs of Arizona said on a radio show last week: “I think it’s time for Dr Fauci to move along … He’s emasculated the economy and is just totally tone-deaf on that.”

The far-right commentator Laura Ingraham complained last week that it was “time to get your freedom back”, tweeting footage of people sitting in a line of cars in a Michigan protest against social distancing. The more extreme critics accuse Fauci of being a “deep state plant” with a shadowy agenda.

It is not the first time Fauci has encountered blowback from telling hard scientific truths.

“Decades ago, he said things that we didn’t want to hear,” said Hodel, the Aids activist. “He said a lot of things we did want to hear as well, but he said a lot of things we didn’t want to hear, about the pace of research, about the inability to pull a cure out of his hat, about the need for safe sex, early on.”

As a boy in Brooklyn growing up in the postwar boom years, Fauci delivered prescriptions on his bicycle for the family business, a pharmacy. He went to Catholic schools and at 5ft 7in was a standout basketball star. He was awarded the presidential medal of freedom, the nation’s highest civilian honor, in 2008. Fauci has been married 35 years, has three daughters, is an avid jogger and – in contrast to the “executive time” loving president – is also a notoriously industrious worker who frequently clocks 15 hour days.

On his philosophy for working with political leaders, Fauci has told the New Yorker’s Michael Specter that he “relies on the pseudo-Latin expression Illegitimi non carborundum: don’t let the bastards grind you down.

“You stay completely apolitical and non-ideological, and you stick to what it is that you do,” Fauci said. “I’m a scientist and I’m a physician. And that’s it.”

An adamant 78% majority of Americans approves of Fauci’s performance, according to a Quinnipiac poll this month that found Trump’s approval rating at 46%.

Hodel said Fauci was motivated by a lifelong dedication to science and by an equal dedication to people.

“I have great confidence in Dr Fauci’s ability to maintain his integrity and to speak the truth. And this is probably not the first time that his career was at risk. I can also say with great confidence that when history is written, Dr Fauci will be the hero.”