Trump announces new impeachment legal team

Republicans are increasingly supportive of the belief that this trial is unconstitutional, and at least one will challenge the proceedings Tuesday.

Just before the Senate breaks for lunch around noon, Sen. Rand Paul, R-Ky., will have about 15 minutes to make his argument as to why he thinks the impeachment trial is unconstitutional. He could raise a constitutional point of order -- which should spark a vote -- forcing senators to go on the record which could signal for the first time where most Republicans stand on convicting Trump.

On Tuesday afternoon, constitutional law professor Jonathan Turley -- who was called as a witness by Republicans in Trump's first impeachment trial and argued against his impeachment then -- has been invited to speak at the weekly closed-door GOP lunch. While it isn't clear if Senate Minority Leader Mitch McConnell was involved in inviting Turley, he likely wouldn't be at the Capitol Hill lunch if McConnell disapproved. 

Turley recently wrote that "retroactive impeachment" -- or impeachment or a former president -- is not constitutional. However, the professor himself noted that he has changed his views over time and previously thought it was constitutional.

The absence of Supreme Court Chief Justice John Roberts is another a key factor in many Republicans' case against the legitimacy of the proceedings as Sen. Patrick Leahy, D-Vt., is set to preside over the swearing-in of senators as jurors Tuesday afternoon.

-ABC News' Trish Turner and Devin Dwyer

House impeachment managers on Monday delivered an article of impeachment against former President Donald Trump to the Senate, queuing up an unprecedented second trial and the first ever for a former president in the chamber.

The managers silently walked the article across the Capitol in the evening -- from the House to the Senate -- where senators, only three Republicans, awaited their arrival before lead impeachment manager Jamie Raskin, D-Md., read it aloud.

The Senate will reconvene on Tuesday for senators to be sworn in as jurors and the "issuance of summons" to Trump, although his trial is not expected to start until Feb. 9 -- an agreement made by Senate leaders to give Trump's defense team time to prepare and the Senate more the opportunity to confirm more of Biden's Cabinet picks.

In order to convict Trump by a two-thirds majority, at least 17 Republican senators would need to join all 50 Democratic senators -- a long-shot since several Republicans have aired grievances with the impeachment process but not with the actions of the former president. Rand Paul, R-Ky., is already expected to object to the proceedings.

Dividing its time, the Senate voted on Monday to confirm of Biden's Treasury Secretary Janet Yellen -- placing the first woman to lead the department. Yellen is Biden's third Cabinet pick to be confirmed -- as the administration continues to lag behind others in confirmations -- and will receive a ceremonial swearing-in at the White House from the nation's first female vice president Tuesday.

The Senate is expected to vote on Anthony Blinken to lead the State Department Tuesday and Alejandro Nicholas Mayorkas to lead the Homeland Security Department, as well as consider the nomination of Rhode Island Gov. Gina Marie Raimondo as Biden's commerce secretary.

Biden makes afternoon remarks outlining his racial equity agenda and signs more executive actions in the afternoon. He has already taken 33 executive actions -- executive orders, proclamations and more -- and 23 of them have aimed to reverse, roll back or just generally undo the Trump agenda, in areas ranging from climate change and COVID-19 to allowing transgender people to openly service in the military.

Domestic Policy Adviser Susan Rice will appear with White House press secretary Jen Psaki at her daily press briefing at 12:30 p.m.

In his first official public endorsement since leaving office, former President Donald Trump backed Sarah Huckabee Sanders' campaign for governor of Arkansas on Monday, hours after the former White House press secretary officially announced her bid. 

Trump released the statement backing Sanders via his new political action committee, Save America, calling his former aide "a warrior who will always fight for the people of Arkansas and do what is right, not what is politically correct."

"Sarah will be a GREAT Governor, and she has my Complete and Total Endorsement!" the statement reads.

Trump had previously publicly encouraged Sanders to run for governor.

-ABC News' Will Steakin

Senate Minority Leader Mitch McConnell said Monday night that he will allow the Senate power-sharing agreement brokered with Majority Leader Chuck Schumer to go forward, solidifying how the evenly tied Senate will function for the next two years.

Specific details of the agreement are not yet clear, but McConnell cites statements from two Democratic members -- Sen. Joe Manchin, D-W.Va. and Sen. Kyrsten Sinema, D-Ariz -- who have said they will not vote to overturn the Senate filibuster rule as the reason he is allowing the agreement to move forward.

Progress on reaching a power-sharing agreement stalled when McConnell announced he wanted assurances from Schumer that he would not overturn the filibuster rule. If Schumer had wanted to do this it would have required the unanimous support of his caucus.

"The legislative filibuster was a key part of the foundation beneath the Senate's last 50-50 power-sharing agreement in 2001. With these assurances, I look forward to moving ahead with a power-sharing agreement modeled on that precedent," McConnell wrote in a statement.

Justin Goodman, a Schumer spokesperson, released a statement in response to the move.

"We're glad Senator McConnell threw in the towel and gave up on his ridiculous demand. We look forward to organizing the Senate under Democratic control and start getting big, bold things done for the American people," Goodman said in the statement.

--ABC News' Allison Pecorin