“It’s obviously a very different situation. It's complete transparency,” Fauci said in an interview Thursday. “Nobody is telling you what to say, at all. They are just saying go out there and let the data guide you on what you are saying."

A fixture at Trump’s White House press conferences during the early weeks of the pandemic, Fauci soon found himself shunted to the side. Now he’s back in the spotlight.

Now the scientist has become the first administration official to face the White House press briefing room. There, on Thursday afternoon, he reiterated the president’s ambitious goal of vaccinating 100 million Americans during his first 100 days in office. Fauci also spoke frankly about the potential threat of new virus variants identified in South Africa, Brazil and the United Kingdom, and about the change in administration.

"There were things that were said, be it regarding things like hydroxychloroquine and other things like that, that really was an uncomfortable thing because they were not based on scientific fact," Fauci said of the Trump administration. "I can tell you, I take no pleasure at all being in a situation with contradicting the president."

It’s already been a long first full day in the Biden administration for Fauci, who addressed the World Health Organization at 4 a.m. Thursday, hours after the U.S. rejoined the global group. He later met with top advisers on Biden’s pandemic playbook.

Fauci has expressed confidence in on Biden’s ambitious vaccination goal despite some tempering of expectations in recent days by other top officials. Biden himself said last week that the administration would need to “move heaven and earth” to hit the target. “This will be one of the most challenging operational efforts we have ever undertaken as a nation,” the president said while laying out his plan to reach vulnerable populations and boost administration sites.

And early Thursday morning, the newly installed director of the Centers for Disease Control and Prevention said she did not think Covid-19 vaccines would be widely available in pharmacies by early March, as top Trump officials had promised.

Biden officials admit that they have learned about Warp Speed hitches in real time, including news last week that the federal reserves of Covid-19 vaccines are exhausted. A massive part of the national vaccination effort relies on vaccines still in the pipeline, such as Johnson & Johnson’s single-dose shot and AstraZeneca’s cheaper two-dose option, which are in final trials to prove they are safe and effective.

Fauci noted that the president is opening up new avenues for vaccination including community health centers, additional pharmacies and mobile units for hard-to-reach populations. Plus, Biden has promised to invoke the Defense Production Act to eliminate bottlenecks in the supply of key equipment like syringes and needles, he said.

“If you look at what General [Gustave] Perna, is telling us about what’s going to be coming in in the next three months, I believe we are going to make that goal,” said Fauci, referencing one of the leads on the national distribution effort, known in the Trump era as Operation Warp Speed.

The scientist told POLITICO that he also sees his role as repairing some international relations left in tatters after the Trump presidency.

“When you deal with a global pandemic, you have to have global connectivity, cooperation, collaboration and solidarity. That was one of the first things that the president wanted to make sure happened,” Fauci said.

His long relationship with World Health Organization Secretary-General Tedros Adhanom Ghebreyesus and involvement in the global HIV efforts led the Biden administration to tap him as chief medical advisor, Fauci said. But he is far from leaving his post as the director of the National Institutes of Health’s infectious disease department.

“I was just the messenger of the president,” the health care veteran said. “I’ll just do what I can do to make things better and get things on track.”