State Dept. condemns arrests, repression in Russia

Biden is waking up in the White House for the first time as 46th president of the United States and Vice President Kamala Harris to the fact that for the first time in American history a woman is serving as vice president.

After a historic inauguration, they'll start the day alongside their spouses with an inaugural prayer service from the Washington National Cathedral but attending virtually from the White House Blue Room. Their first full day in office will focus on the coronavirus pandemic, with Biden set to deliver afternoon remarks on his administration's COVID-19 response, take 10 executive actions aimed to control the pandemic and receive a COVID-19 briefing.

Ahead of introducing what it has deemed the "National Strategy for the COVID-19 Response and Pandemic Preparedness," the Biden administration addressed other top priorities overnight including moving to halt deportations of certain non-citizens for 100 days to review immigration policies. The president on Wednesday took at least 15 executive actions from invoking a mask mandate on federal properties and reversing now former President Donald Trump's Muslim ban to moving to rejoin both the World Health Organization and the Paris Climate Accord, barreling faster to dismantle his predecessor's legacy than other modern presidents.

Biden and Harris are taking office amid a racial-justice reckoning, a struggling economy and with the systems of government having come under literal attack by supporters of the man they defeated. While Wednesday's inaugural festivities saw powerful musical performances and poetry, amid history-making formalities, the surreal fact lingered: They took the office on the same Capitol steps that violent pro-Trump protesters climbed to storm the halls of Congress precisely two weeks earlier.

In the wake of the seige and in their first days of office, Biden and Harris will also have to contend with Trump's impeachment trial which will be taken up in the newly Democratic Senate as soon as the end of this week, competing for floor time with their legislative agenda and Cabinet confirmations.

The United States will remain a member of the World Health Organization, Dr. Anthony Fauci, the nation's leading infectious disease expert, announced Thursday.

Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, made the announcement via video link to the WHO's executive board in Geneva, a day after Joe Biden was sworn-in as the 46th president of the U.S.

"I am honored to announce the United States will remain a member of the World Health Organization," Fauci told the board Thursday, adding that the U.S. will also "fulfil its financial obligations" to the WHO and stop reducing its staff at the United Nations agency.

Fauci, who is Biden's chief medical adviser on the coronavirus pandemic, also announced that the president will issue a directive Thursday that shows the country's intent to join the COVAX Facility, a global initiative to ensure rapid and equitable access to COVID-19 vaccines for all countries regardless of income.

Within hours of becoming president, Biden had signed an executive order reversing former President Donald Trump's decision to withdraw from the WHO. Trump had accused the organization of failing to correctly respond to the coronavirus pandemic and of allegedly giving too much power to China.

In an interview Thursday with ABC News' Michael Strahan on "Good Morning America," Fauci said rejoining the WHO is "very important" and that the country's withdrawal "was very disconcerting to everybody."

"When you're dealing with global pandemic, you have to have an international connectivity, and for us to not be in the WHO was very disconcerting to everybody, all the member countries including the health officials here in the United States," he said. "So the official announcement that we are rejoining, we're going to live up to our financial commitments and a whole bunch of other things, it was really a very good day. I mean, the response I'm getting from my colleagues all over the world is really very refreshing."

-ABC News' Morgan Winsor

The president and first lady emerged from the White House shortly before 10 p.m. to watch a fireworks display that ended the inaugural festivities on Wednesday night.

While the Bidens were on the Blue Room Balcony, the vice president and second gentleman watched from the steps of the Lincoln Memorial, where Harris had spoken to the public a few minutes earlier and where Katy Perry was performing her song, "Firework."

In a show of unity and bipartisanship, the three former president who attended Wednesday's inauguration recorded a video while they were at Arlington National Cemetery earlier in the day.

Former President Barack Obama kicked off the discussion, noting his pride in watching his former vice president and the first Black, South Asian American and female vice president being sworn into office. Then the group turned to address the day’s theme of unity.

“I think that the fact that the three of us are standing here talking about a peaceful transfer of power speaks to the institutional integrity of our country,” said former President George W. Bush.

He also called on Americans to love one another the way they'd like to be loved, while former President Bill Clinton said more directly, that "everybody needs to get off their high horse and reach out to their friend and neighbors to try to make it possible."

The three former presidents ended the video by offering some parting words to Biden.

"Mr. President, I'm pulling for your success. Your success is our country's success," Bush said, paraphrasing a message his father left for Clinton during their transition.

"I'm glad you're there," Clinton said. "And I wish you well. You have spoken for us today. Now you will lead for us and we're ready to march with you."

And Obama told his former vice president that they’d all be there for him.

“Joe, I'm proud of you. And you and Kamala need to know that you've got all of us here rooting for your success, keeping you in our prayers, and we will be available in any ways that we can as citizens to help you guide our country forward," Obama said. "We wish you godspeed.”

-ABC News' Molly Nagle and Justin Gomez