Trump announces new impeachment legal team

Incoming Defense Secretary Lloyd Austin -- the Defense Department's first Black chief -- was ceremonially sworn in by Vice President Kamala Harris -- the nation's first Black vice president -- in the Roosevelt Rom of the White House on Monday afternoon.

Austin's wife, Carlene, held the Bible her husband placed his hand upon for the ceremony.

Moments earlier, Austin stood alongside Biden in the Oval Office as the president signed an executive order stating all Americans, regardless of gender identity, can serve in the Armed Forces.

“I fully support the President’s direction that all transgender individuals who wish to serve in the United States military and can meet the appropriate standards shall be able to do so openly and free from discrimination," Austin said in a statement Monday.

-ABC News' Matthew Seyler

Sen. Patrick Leahy, D-Vt. -- the Senate president pro tempore -- is expected to preside over the impeachment trial of former President Donald Trump.

Senators preside when the impeached person is not the president of the United States, according to a Senate source.

The trial is slated to begin the week of Feb. 8 following House impeachment managers delivering the article of impeachment for "incitement of insurrection" to the Senate Monday evening.

Supreme Court Chief Justice John Roberts presided over Trump's last impeachment trial.

-ABC News' Trish Turner

Biden has officially reversed a ban on transgender people from serving in the U.S. military, signing an executive order in a brief ceremony in the Oval Office with Defense Secretary Lloyd Austin and Joint Chiefs Chairman Mark Milly looking on.

"What I'm doing is enabling all qualified Americans to serve their country in uniform," he said.

The White House had announced earlier he had done so in a release.

The controversial ban was put in place by former President Donald Trump in 2017 and reversed the Obama administration’s policy to allow open service by transgender people.

-ABC News' John Verhovek

Clarification: This story has been updated to reflect that the White House press release was issued before the actual signing.

As Biden assumes his first full week in office, he enters with only two Senate confirmed appointees -- lagging behind previous administrations in having Cabinet nominees confirmed.

The Senate convenes at 3 p.m. on Monday and will continue considering the nomination of Janet Yellen to be treasury secretary ahead of an evening vote.

After that, House impeachment managers will walk over and read the article of impeachment against former President Donald Trump to the Senate. The trial isn't slated to start until Feb. 8 to give Trump's defense time to prepare and Biden the chance to have his nominees confirmed and spending priorities addressed in the Senate.

On the campaign trail, Biden guaranteed his White House would "look like the country." Half of Biden's Cabinet picks are women, and the majority are people of color. Biden has noted that many of his selections would be pioneers in their roles -- including the first woman to serve as treasury secretary, the first Black defense secretary, the first openly gay man confirmed to a Cabinet role and the first Native American Cabinet secretary.

Last week, Avril Haines was confirmed as the first female Director of National Intelligence and Lloyd Austin as the first Black Pentagon chief.