Biden and Vice President-elect Kamala Harris will introduce key picks for their science team in Wilmington, Delaware, Saturday afternoon.

The picks are:

-Eric Lander: Nominee for director of the Office of Science and Technology Policy (OSTP) and presidential science advisor-designate.

-Alondra Nelson: OSTP deputy director for science and society

-Frances H. Arnold: Co-chair of the President’s Council of Advisors on Science and Technology (PCAST)

-Maria Zuber: Co-chair of the President’s Council of Advisors on Science and Technology (PCAST)

In a press release, the Biden transition team said the picks will help the Biden-Harris administration "confront some of the biggest crises and challenges of our time, from climate change and the impact of technology on society to pandemics, racial inequity, and the current historic economic downturn."

Biden has announced a new slate of nominations and staff at the Department of State. Many of the picks have ties to both Biden and former President Barack Obama.

The picks are:

-Wendy R. Sherman: Deputy secretary of state

-Brian P. McKeon: Deputy secretary for management and resources

-Bonnie Jenkins: Under secretary for arms control and international security affairs

-Victoria Nuland: Under secretary for political affairs

-Uzra Zeya: Under secretary for civilian security, democracy, and human rights

In a statement, the Biden transition team said these key nominations will help "build back better at the State Department, renew and reimagine American leadership to keep us safe at home and abroad, and address the defining challenges of our time — from infectious disease, to terrorism, China, nuclear proliferation, cyber threats, and climate change. They will put into practice the President-elect and Secretary-designate’s vision of a foreign policy that promotes America’s security, prosperity, and values, and delivers for the middle class."

-ABC News' Beatrice Peterson

Late Friday, Health and Human Services Secretary Alex Azar refuted several media reports that he was resigning early, but did share his resignation letter -- effective Jan. 20 at noon -- on Twitter.

While Azar wrote on Twitter that it was his "duty to help ensure a smooth transition to President-elect Biden’s team during the pandemic" through Inauguration Day, he did criticize President Donald Trump and called on him to more strongly condemn the violence at the Capitol last week.

"Unfortunately, the actions and rhetoric following the election, especially during this past week, threaten to tarnish these and other historic legacies of this Administration," Azar wrote in the resignation letter. "The attacks on the Capitol were an assault on our democracy and on the tradition of peaceful transitions of power that the United States of America first brought to the world. I implore you to continue to condemn unequivocally any form of violence, to demand that no one attempt to disrupt the inaugural activities in Washington or elsewhere, and to continue to support unreservedly the peaceful and orderly transition of power on January 20, 2021."

Azar clarified he handed in the letter, dated Jan. 12, last week "along with every other political appointee."

The two-page letter, in which he calls serving as HHS secretary "the greatest professional privilege and honor of my life," details the administration's response to the coronavirus pandemic. Azar paints an entirely rosy picture, referring to it as a "remarkable response," despite skyrocketing deaths and case rates across most of the nation.

"While we mourn every lost life, our early, aggressive, and comprehensive efforts saved hundreds of thousands or even millions of American lives," he wrote, echoing a refrain from the president. There have been over 391,000 deaths in the U.S., nearly twice the number of the second-highest country (208,000 in Brazil).

He also highlighted the agency's efforts to combat the opioid crisis, electronic cigarettes and the HIV epidemic, and made special mention of "protect[ing] the sanctity of human life from conception to natural death."

Azar has served as HHS secretary since January 2018. President-elect Joe Biden has nominated Xavier Becerra, California's attorney general, to serve as his HHS chief.

ABC News' Ben Siu contributed to this report.

Barry Berke, the veteran New York defense lawyer who helped House Democrats argue President Donald Trump's first impeachment last year, will rejoin the House Judiciary Committee as the panel's lead impeachment lawyer for Trump's second trial, the panel announced Friday.

Berke will serve as chief impeachment counsel, supported by a team of attorneys from the House Judiciary and Oversight committees who helped Democrats make their case to the Senate last year that Trump abused his office by trying to pressure Ukraine's president to dig up dirt on then-candidate Joe Biden.

While House Speaker Nancy Pelosi, D-Calif., unveiled a team of nine new impeachment managers to make the case that Trump should be convicted of inciting the Capitol Hill riot that left five people dead, the presence of Berke and the rest of the legal team underscores the unique position House Democrats are in: For the first time in American history, they will have a team of lawyers behind them with experience arguing in a Senate impeachment trial.

Democrats could transmit the impeachment article to the Senate as early as next week, which could trigger the start of proceedings following Biden's inauguration on Wednesday.

There has been no official announcement on who will represent Trump in the trial, but personal lawyer Rudy Giuliani and Alan Dershowitz, who took part in the last trial, may be on the team, sources told ABC News. Trump favorite John Eastman, who led a failed election challenge to the Supreme Court, could also join the team.

-ABC News' Katherine Faulders and Benjamin Siegel

Senate Majority Leader Mitch McConnell has indicated that the Senate impeachment trial should take place after Trump leaves office.

The Senate impeachment process will begin "at our first regular meeting following receipt of the article from the House," McConnell wrote in a new statement, saying he believes it would be best for the country to have an orderly transfer of power completed before a trial begins.

The Senate is currently scheduled to return to Washington on Tuesday, making that the earliest day for any Senate action related to the trial to occur -- but McConnell's message to House Speaker Nancy Pelosi and Democrats is for them not to send the articles until after Biden is sworn in.

McConnell has no control over when a trial begins -- that is determined by the articles sent to the Senate​​.

While House Speaker Nancy Pelosi has so far declined to say publicly when the House will send the article over to the Senate, a source involved in the Democratic leadership deliberations told ABC News earlier Wednesday Pelosi planned to send the article to the Senate next week.

"Even if the Senate process were to begin this week and move promptly, no final verdict would be reached until after President Trump had left office. This is not a decision I am making; it is a fact. The President-elect himself stated last week that his inauguration on January 20 is the ‘quickest’ path for any change in the occupant of the presidency," McConnell wrote.

"In light of this reality, I believe it will best serve our nation if Congress and the executive branch spend the next seven days completely focused on facilitating a safe inauguration and an orderly transfer of power to the incoming Biden Administration."

McConnell confirmed on the record earlier Wednesday that he is considering voting to convict Trump on inciting an insurrection.

-ABC News' Allison Pecorin