Photo: The Canadian Press

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, takes questions as he speaks with reporters in the James Brady Press Briefing Room at the White House, Thursday, Jan. 21, 2021, in Washington.

Dr. Anthony Fauci is back.

In truth, the nation’s leading infectious-diseases expert never really went away. But after enduring nearly a year of darts and undermining comments from former President Donald Trump, Fauci now speaks with the authority of the White House again.

He called it “liberating” Thursday to be backed by a science-friendly administration that has embraced his recommendations to battle COVID-19.

“One of the new things in this administration is, If you don’t know the answer, don’t guess,” Fauci said in one pointed observation during a White House briefing. “Just say you don’t know the answer.”

Fauci’s highly visible schedule on Thursday, the first full day of President Joe Biden’s term, underscored the new administration's confidence in the doctor but also the urgency of the moment.

His day began with a 4 a.m. virtual meeting with officials of the World Health Organization, which is based in Switzerland, and stretched past a 4 p.m. appearance at the lectern in the White House briefing room.

The breakneck pace showcased the urgent need to combat a pandemic that has killed more than 400,000 Americans and reached its deadliest phase just as the new president comes to office.

Fauci made clear that he believed the new administration would not trade in the mixed messages that so often came from the Trump White House, where scientific fact was often obscured by the president’s political agenda.

“The idea that you can get up here and talk about what you know and what the science is ... it is something of a liberating feeling,” Fauci told reporters. White House press secretary Jen Psaki had invited Fauci to take the podium first at her daily briefing.

While choosing his words carefully, Fauci acknowledged that it had been difficult at times to work for Trump, who repeatedly played down the severity of the pandemic, refused to consistently promote mask-wearing and often touted unproven scientific remedies, including a malaria drug and even injecting disinfectant.

“It was very clear that there were things that were said, be it regarding things like hydroxychloroquine and other things, that really was uncomfortable because they were not based in scientific fact,” Fauci said. He added that he took “no pleasure” in having to contradict the president, a move that often drew Trump’s wrath.

Biden, during his presidential campaign, pledged to making Fauci his chief medical adviser when he took office, and the 80-year-old scientist was immediately in motion.