Trump impeachment trial live updates: Biden says charge 'not in dispute' in 1st comments on acquittal

Inside the Senate chamber, some senators have been listening intently and taking notes, while others chatted with each other or moved in and out of the chamber.

One moment when everyone in the chamber seemed to turn to pay attention -- including Sen. Josh Hawley, R-Mo., up in the gallery and those on the floor who were otherwise distracted: When House manager Rep. Joe Neguse quoted rioters saying they were inspired by Trump. Neguse showed slides of tweets and news stories and played clips of video.

After this moment played out and Neguse turned it over to Rep. Joaquin Castro, D-Texas, there was a lot of shuffling in the chamber and a number of senators got up to go to their respective cloakrooms.

Two of Trump’s staunchest allies left the floor to confer: Sens. Lindsey Graham, R-S.C., rose and tapped Ted Cruz, R-Texas, on the shoulder. They then stood in the cloakroom, in view of reporters through the glass in the doors, and spoke for several minutes.

Of all senators taking notes, Sen. Bill Cassidy, R-La., was the most notable -- he voted with Democrats Tuesday night and said he was approaching the trial as an impartial juror. He wrote vigorously and almost unceasingly until a break was called.

Sen. Ben Sasse, R-Neb., also took notes on a stack of small notecards. When videos of protesters shouting "stop the steal" were shown by House managers, almost all of the members looked up at the screen. The senators seemed less interested during videos of president Trump.

Rep. Eric Swalwell, D-Calif., read a tweet of Trump's that mentioned Senate Minority Leader Mitch McConnell and Sens. John Thune, R-S.D., and John Cornyn, R-Texas., by name. When the tweet was read, Cornyn looked directly at Thune. But Thune stared straight ahead at the screen. McConnell was stoic and remained still. 

-ABC News' Allison Pecorin and Kathrine Faulders

Congresswoman Stacey Plaskett, D-Virgin Islands, was tasked with arguing the case for how Trump was aware of the violence on Jan. 6 and amplified supporters' plans for insurrection instead of calling them off, a pattern the president had already established in his repeated refusals to directly denounce violence in his presidency, she said.

"Some of you have said there's no way the president could have known how violent the mob would be. That is false, because the violence, it was foreseeable," Plaskett said. "The violence that occurred on Jan. 6 -- like the attack itself -- did not just appear. You'll see that Donald Trump knew the people he was inciting. He saw the violence that they were capable of, and he had a pattern and practice of praising and encouraging that violence never, ever condemning it."

"This violent attack was not planned in secret," Plaskett continued, noting many rioters -- whom she referred to as "Trump's cavalry" -- were proud to be a part of the attack. "The insurgents believed that they were doing the duty of their president. They were following his orders, and so they publicized it openly, loudly, proudly -- exact blueprints of how the attack would be made."

"He fanned the flame of violence and it worked," she said. "There are many examples where the president engaged in this pattern and I'm just going to walk you through a few of them."

Plaskett went on to tick through instances to support the managers' case including Trump calling on the Proud Boys to "stand back and stand by" in the first 2020 presidential debate -- instead of denouncing them -- and tweeting videos praising his supporters attempting to drive a Biden campaign bus off the road ahead of the election.

Lead impeachment manager Rep. Jamie Raskin, D-Md., in introducing Plaskett called it a moment of "special pride" because Plaslett is not only the first delegate ever to be on a team of impeachment managers in American history, but she is also but also Raskin's former law student.

House manager Rep. Ted Lieu, D-Calif., argued that Trump incited the violent rioters on Jan. 6 after many other attempts to overturn the election.

"President Donald J. Trump ran out of non-violent options to maintain power. After his efforts in the courts and threatening officials failed, he turned to privately and publicly attacking members of his own party in the House and in the Senate," Lieu said. "He would publicly bait senators, naming them in social media."

Lieu discussed how Trump pressured senators, state election officials and even his own Vice President Mike Pence to overturn the results.

"Vice president Pence showed us what it means to be an American, what it means to show courage. He put his country, his oath, his values, and his morals above the will of one man," Lieu said. "The president had tried everything in his power to seize -- everything in his attempt to seize power from the rightful victor of the election, president Trump's extraordinary actions grew increasingly more desperate."

Sen. Bill Cassidy, R-La., is facing criticism from his home state party for his vote siding with Democrats in favor of the constitutionality of impeachment.

"The Republican Party of Louisiana is profoundly disappointed by Senator Bill Cassidy's vote on the constitutionality of the impeachment trial now underway against former President, now private citizen, Donald J. Trump," the statement says. 

Cassidy told reporters Tuesday night that he is an "impartial juror," and he voted in favor of the constitutionality after the compelling argument made by House managers.

The statement from the Louisiana GOP further echoes what many Trump backers, in the lead-up to the trial, have said -- that impeaching a private citizen "is not only an unconstitutional act, but also an attack on the very foundation of American democracy."

-ABC News' Alisa Wiersema