The Senate is taking a 10-minute break following the arguments from the House impeachment managers. Trump's legal team will take the floor next.

-ABC News' Benjamin Siegel

House manager Rep. Joe Neguse, D-Colo., discussed a precedent debated among conservative legal experts about the Senate holding a trial for Secretary of War William Belknap in 1876.

Belknap resigned his post days before a House vote in an unsuccessful attempt to avoid impeachment.

"And when his case reached the Senate, this body, Belknap made the exact same argument that president Trump is making today. That you all lack jurisdiction, any power to try him, because he's a former official. Now, many senators at that time when they heard that argument, literally they were sitting in the same chairs you all are sitting in today. They were outraged by that argument, outraged. You can read their comments in the record," Neguse said. "They knew it was a dangerous, dangerous argument with dangerous implications."

Neguse also cited comments from a co-founder of the conservative Federalist Society and Republican lawyer Charles Cooper arguing that a former president can be impeached. Neguse also cited Jonathan Turley's writings about impeachment during the impeachment trial of former President Clinton, which he has since disavowed, given that he now opposes impeaching Trump as a former president.

"What you experienced that day, what we experienced that day, what our country experienced that day, is the framers' worst nightmare come to life. Presidents can't inflame insurrection in their final weeks and then walk away like nothing happened," Neguse said. "And yet, that is the rule that president Trump asks you to adopt."

-ABC News' Benjamin Siegel

Breaking the silence in the chamber after playing out the managers' first video, lead House impeachment manager Rep. Jamie Raskin said, "If that's not an impeachable offense, then there is no such thing."

Raskin also made an appeal to senators' interest in defending the prerogatives of the legislative branch: If they acquit Trump, they will be ceding power to the executive branch.

"If the president's arguments for a January exception are upheld, then even if everyone agrees that he's culpable for these events, even if the evidence proves, as we think it definitively does, that the president incited a violent insurrection on the day Congress met to finalize the presidential election, he would have you believe there is absolutely nothing the Senate can do about it. No trial, no facts. He wants you to decide that the Senate is powerless at that point. That can't be right," he said.

Citing the impeachment of Warren Hastings in the Parliament of Great Britain, Raskin said the Framers of the Constitution supported impeaching former officials. He also said the power of Congress to impeach, convict and disqualify a president from holding future office are needed the most during a transfer of power, Raskin argued, adding, "That's precisely when we need them the most, because that's when elections get attacked."

"Given the Framers' intense focus on danger to elections and the peaceful transfer of power, it is inconceivable that they designed impeachment to be a dead letter in the president's final days in office when opportunities to interfere with the peaceful transfer of power would be most tempting and most dangerous, as we just saw," he said.

Rep. Joe Neguse, D-Colo., took the floor after Raskin.

-ABC News Benjamin Siegel

Inside the Senate's first impeachment trial of a former president -- and the first during a global pandemic -- a pool of reporters were permitted to cycle inside, one at a time to witness the floor activity not necessarily captured by cameras stationed there.

ABC News' Trish Turner noted that every senator was in the chamber for the start. Republicans could be seen handing in their electronics as they entered the chamber though the GOP cloakroom as phones are not allowed during the trial. 

At the Trump legal team desk, closest to the lectern, sat Trump's four attorneys: David Schoen, Bruce Castor, Michael van der Veen and Julieanne Bateman, along with a legal aide. At the House managers table sat Rep. Jamie Raskin, D-Md., with counsel Barry Berke and a legal aide.

Schoen and Sen. Patrick Leahy, D-Vt., the president pro tempore presiding over the trial, made small talk before the trial started.

All senators were masked up but a handful including Sen. Cynthia Lummis, R-Wyo., Sen. James Risch, R-Wis., and Sen. Rand Paul, R-Ky.

Van der veen was the only lawyer at the Trump table reading and marking up documents. The others each sat with a blank, yellow legal pad.

When asked if they were an opponent or proponent of the constitutional question, Raskin and then Castor said, "We're a proponent" and "We're an opponent," respectively.

Another reporter from the pool described the atmosphere in the chamber as "incredibly tense" while senators watched the video compilation from Raskin of the assault on the Capitol.

Almost every senator was watching the video, most wearing frowns, the reporter noted, and the sounds of the video appeared to echo in the chamber, "filling it with the screams and yells of the mob."

-ABC News' Trish Turner