Tensions with Trump: Dr. Anthony Fauci on telling the truth The respected scientist is now a real-time fact-checker to the president.

Just as those free-wheeling daily White House briefings on how the government is dealing with the coronavirus have become a constant in this strange new iteration of American life, so, too, has the presence of Dr. Anthony Fauci as a real-time fact-checker to President Donald Trump.

Fauci, the government’s top expert on infectious diseases, has long been viewed as a truth-teller, but never so much as now, reassuring Americans looking for science-based answers about what to expect in the coronavirus epidemic, using plain-spoken language in his trademark Brooklyn accent.

But he was not on the White House briefing room stage Monday evening, when Trump strongly suggested he wanted to scale back -- in weeks, not months -- the guidelines that have led to much of the nation shutting down. That's much sooner than Fauci and other public health experts have estimated is needed to keep the disease spread from getting drastically worse.

Trump said Fauci's recommendation would be "very important" to him but he alone would make the final decision. Fauci, Trump said, instead of standing next to him as before, had been at a coronavirus task force meeting as he spoke. "He's a good man. I like Dr. Fauci a lot, just so you understand," Trump told reporters.

Now 79, Fauci has helped lead the nation against HIV-AIDS and other crises over decades but none has tested his political skills like this one -- under Trump.

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Increasingly, the science guiding Fauci has led him to directly and publicly counter with the president — a leader who has fired or forced out dozens of administration officials who have contradicted him or seemed to steal his spotlight.

The tensions have been evident -- as much has he's tried to deal with them diplomatically. Now, he's explained their differences in some of his most candid terms yet.

Though Fauci said he doesn't disagree in "substance" with language used during the coronavirus task force briefings, “it is expressed in a way that I would not express it, because it could lead to some misunderstanding about what the facts are about a given subject,” Fauci told Science Magazine in an interview.

Fauci addressed the widening gap between his research-based views and the president’s unsubstantiated optimism.

In recent days, they’ve most publicly disagreed on a medication that Trump said he hopes — without evidence, as Fauci has clarified — will treat coronavirus.

On Thursday, Trump declared an anti-malaria drug could be a “game changer” in the effort to develop a coronavirus treatment and announced the drug had been “approved.” The drug, called chloroquine, or hydroxychloroquine, indeed has been approved -- since 1944 -- but to treat and prevent malaria. No drug has been approved to treat COVID-19, and a vaccine is estimated to remain at least a year away.

When asked if the drug was promising Friday, Fauci, standing next to Trump, said “the answer is no” because “the evidence you’re talking about … is anecdotal evidence.”

Fauci was also seen raising his hand to his temple as the president told reporters that Secretary of State Mike Pompeo would be leaving the briefing early to return to the “the State Department, or as they call it the Deep State Department.”

Asked if he’d been criticized later for the gesture, which was caught on television and widely circulated in internet memes as evidence of Fauci’s disagreement with the president, Fauci told Science, “No comment."

In another instance, the president suggested that China's government could have shared details about a new coronavirus epidemic months earlier than it did. Fauci has publicly knocked that assertion down, which he said “doesn’t comport” with the facts, and explained the behind-the-scenes efforts to tamp down that narrative.

He told the "appropriate people," he said, who passed along the message. He explained his means — and limits — in correcting the president.

“The next time they sit down with him and talk about what he’s going to say, they will say, ‘By the way, Mr. President, be careful about this and don’t say that.’,” Fauci said. “But I can’t jump in front of the microphone and push him down. OK, he said it. Let’s try and get it corrected for the next time,” Fauci told Science.

Given the volatility of Trump’s administration, which has an 82% turnover rate among senior advisers, according to research by the nonprofit public policy organization the Brookings Institution, Fauci’s outspokenness raises concerns about his future. When he’s missing from a coronavirus task force briefing, questions about his whereabouts immediately flood Twitter.

“How are you managing to not get fired?” Science pointedly asked Fauci in the interview published Monday.

“Well, that’s pretty interesting because to [Trump’s] credit, even though we disagree on some things, he listens. He goes his own way. He has his own style. But on substantive issues, he does listen to what I say,” Fauci said.

Standing next to the president on Saturday, Fauci sought to reconcile his role with what he sees as the president's.

“The president is talking about hope for people. And it’s not an unreasonable thing: to hope for people,” Fauci said, acknowledging the differences between what he and the president said. “And then you have the other group — which is my job, as a scientist, to say my job is to ultimately prove, without a doubt, that a drug is not only safe, but that it actually works.”

“You really got to have a balance," he said. "I’ve got to do my job as a scientist and others have other things to do."

What to know about coronavirus:

How it started and how to protect yourself: coronavirus explained

What to do if you have symptoms: coronavirus symptoms

Tracking the spread in the US and Worldwide: coronavirus map

ABC News' Jordyn Phelps and Anne Flaherty contributed to this report.

This report was featured in the Tuesday, March 24, 2020, episode of “Start Here,” ABC News’ daily news podcast.

"Start Here" offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, Spotify, the ABC News app or wherever you get your podcasts.