Rep. Eric Swalwell, D-Calif., in helping to lay out opening arguments for House impeachment managers, said that Trump's conduct leading up to Jan. 6 was "deliberate, planned and premeditated," matching the criteria for prosecuting a violent crime.

"This was not one speech, not one tweet. It was dozens in rapid succession with the specific details," Swalwell said, displaying tweets and recordings. "In fact, when he had assembled his inflamed mob in D.C., he warned us that he knew what was coming."

"This was one of his dozens of statements on Twitter in the hours leading up to the attack, 'I hope the Democrats and even more importantly the weak and ineffective RINO section of the Republican party are looking at the thousands of people pouring into D.C. They won't stand for a landslide victory to be stolen. @Senatemajorityleader. @Johncornyn. @Senatejohnthune,'" Swawell said, appearing to look at those senators while he said their names. "He tags senators to pressure you to stop this."

"He built this mob over many months with repeated messaging until they believed that they had been robbed of their vote, and they would do anything to stop the certification," Swalwell continued. "He made them believe that their victory was stolen and incited them so he could use them to steal the election for himself."

Swalwell, attempting to appeal to Republican senators, also made a point to say Trump's actions were different than those senators in the room who raised election concerns.

A pool of reporters inside the Senate chamber observed that nearly every seat was filled when the House managers arguments began at noon and that almost every senator wore a mask. One notable absence was Sen. John Hawley, R-Mo.

Some senators, such as Sens. Ben Sasse, R-Neb., Lisa Murkowski, R-Alaska, and and Pat Toomey, R-Pa., intently took notes as the House impeachment managers made this assertions. Though reporters noted that the vast majority of senators appeared to be at least partially engaged with the content arguments from Rep. Raskin, D-Md., and Rep. Joe Neguse, D-Colo.

During the prayer and pledge, as Chaplain Barry Black said, “during this impeachment trial, give our lawmakers the gift of discernment so that they will know truth from falsehood,” several seats on both sides of the aisle were empty. Republicans who were there bowed their heads while standing over their desks, and Democrats, like Sens. Cory Booker, D-N.J. and Maize Hirono, D-Hawaii, were gathered in the back of the chamber.

Sen. Tammy Baldwin, D-Wis., sat on the Republican side talking to Sens. Ron Johnson, R-Wis., and Toomey before going to her seat on the other side of the aisle. After the pledge, once Rep. Jamie Raskin, D-Md., stepped up to the microphone, Democrats and Republicans filed in from the cloakrooms -- some of them still chewing underneath their masks.

Some Republicans came in late, like Sens. Ted Cruz, R-Texas, Roy Blunt, R-Mo., Susan Collins, R-Maine, and James Risch, R-Idaho. Hawley, when he came in alone, watched from the gallery above. He was seen flipping through manila folders and -- at one point -- put his feet up on the desk. He rarely looked at the arguments on the Senate floor.

Senate Minority Leader Mitch McConnell sat with his hands folded in front of him.

When House managers used video exhibits, reporters noted that many GOP senators took notice. During some videos, they described every GOP senator turning and watching the exhibit or reading the exhibits for an extended period of time.

-ABC News' Katherine Faulders

The Senate is taking a 15-minute break following the start of opening arguments from the House impeachment managers.

Rep. Eric Swalwell, D-Calif., laid out the framework for how Trump, in the days after the election continued to falsely tell his supporters the election was "rigged" and "stolen," using a series of Trump's own tweets and remarks to make his point.

"Just like to build a fire, it doesn't just start with the flames, Donald Trump for months and months assembled the tend, the kindling, threw on logs for fuel to have his supporters believe that the only way their victory would be lost was if it was stolen. That way, President Trump was ready if he lost the election to light the match," Swalwell said.

Swalwell went on to remind how some election officials across the country were berated in the weeks following the election and played video of protesters surrounding the secretary of state's house in Michigan.

"There is plenty of evidence to show words have consequences -- and if he wanted to stop it, he could stop it," Swalwell said. "President Trump was never shy about using his platforms to try and stop something. He could have very easily told his supporters, stop threatening officials, stop GOP going to their homes, stop it with the threats. But each time he didn't."

Swalwell said Trump did the "polar opposite" of what anyone else in that chamber would have done had they lost an election. He started running ads falsely claiming election fraud and spent $50 million from his legal defense fund to amplify his message, Swalwell said.

"These ads were designed to run all the way up to Jan. 5, and then, they stopped. This was purposeful and deliberate planning to target his base to rally around that day. And it wasn't just his ads. He continued to use his own platform. He told his supporters who truly believed their victory had been stolen and who were ready to fight when, where and how to stop what he believed was a steal," Swalwell said.

After the Senate decided it will not call any witnesses, lead House manager Rep. Jamie Raskin, D-Md., was the first to speak during closing arguments. He reiterated the prosecution's case, calling for the conviction of Trump.

"It was suggested by defense counsel that Donald Trump's conduct during the attack, as described in Congresswoman Beutler's statement, is somehow not part of the Constitutional offense for which former President Trump has been charged," Raskin began. "I want to reject that falsehood and that fallacy immediately. After he knew that violence was underway at the Capitol, President Trump took actions that further incited the insurgents to be more inflamed and to take even more extreme, selective, and focused action against Vice President Mike Pence."

Raskin went on to use his time to describe Trump's months-long campaign to discredit the 2020 election results by spreading misinformation, which he argued laid the groundwork for deadly events of Jan. 6. He went on to claim that the former president assembled the mob, incited it and then sent it off to the Capitol during his speech. At every point, Trump sided with the insurrectionists rather than the Congress, Raskin said.

Once when the violence began, Raskin declared that Trump ignored the violence and further incited it by aiming the attacks on his own vice president.

"There has never been a greater betrayal by the president of the United States of his office, and of his oath to the Constitution."

Raskin then took a moment to suggest the GOP used "cancel culture" against one of its leaders, Rep. Liz Cheney, R-Wyo., who voted to impeach Trump in the House.

"Liz Cheney is a hero for standing up for the truth, and resisting this retaliatory cancel culture that she was subjected to."

Raskin emphasized his gratitude toward the Capitol Police, and finished his argument by saying convicting Trump is a vote for the "security of our democracy."

"They attacked this building, they disrupted the peaceful transfer of power, they injured and killed people, convinced that they were acting on his instructions, and with his approval, and protection," Raskin finished. "And while that happened, he further incited them, while failing to defend us. If that's not ground for conviction, if that's not a high crime and misdemeanor against the republic in the United States of America then nothing is. President Trump must be convicted for the safety and security of our democracy and our people."