Trump attorney Bruce Castor opened by praising the "outstanding presentation" from House impeachment managers, noting what Rep. Jamie Raskin, D-Md., and his family endured "during that terrible day."

"You will not hear any member of the team representing former President Trump say anything but in the strongest possible way denounce the violence of the rioters and those that breached the Capitol, the very citadel of our democracy, literally the symbol that flashes on television whenever you're trying to explain that we're talking about the United States, instant symbol," Castor said.

Notably, Castor referred to Trump as "the former president," a term the Trump team has avoided using in their press releases.

Castor, a former Montgomery County, Pennsylvania, district attorney faced criticism in that role for declining to prosecute Bill Cosby in 2005.

The Senate returned from a 10-minute break following the arguments from the House impeachment managers.

Trump's legal team has taken the floor with Bruce Castor opening with his argument that it's unconstitutional to put a former president on trial.

House impeachment manager Rep. Jim Cicilline, D-R.I., offered an early rebuttal to arguments expected from Trump's legal team, beginning by arguing that the former president is not merely a private citizen, saying that he "he can and should answer" for his use of power.

Cicilline also read a tweet from Trump that was posted hours after the attack and once again falsely claiming the election was "stripped" from him. Cicilline said that tweet "chills him to the core."

"The president of the United States sided with the insurrectionists, he celebrated their cause, he validated their attack, Cicilline said. "He told them, 'remember this day forever,' hours after they marched through these halls looking to assassinate Vice President Pence, the speaker of the house and any of us they could find."

Cicilline also pushed back on the expected argument that the impeachment is partisan and could enflame partisan tensions.

"They'll assert that this impeachment is partisan and that the spirit of bipartisanship and bipartisan cooperation requires us to drop the case and march forward in unity. With all due respect, every premise and every argument of that conclusion is wrong. Just weeks ago, the president of the United States literally incited an armed attack on the capitol, our seat of government, while seeking to retain power by subverting an election he lost and then celebrated the attack," Cicilline said. "People died, people were brutally injured. President Trump's actions endangered every single member of Congress."

-ABC News' Benjamin Siegel

Rep. Jamie Raskin, D-Md., the lead House impeachment manager, bookended the Democrats opening' arguments on the constitutionality of the trial by recalling how the day impacted him personally, and, fighting back tears, directly called on his colleagues to "not let this be our future."

"Senators, Mr. President, to close I want to say something personal about the stakes of this decision whether President Trump can stand trial and be held to account for inciting insurrection against us," Raskin said. "I hope this trial reminds America how personal democracy is and how personal is the loss of democracy too."

He explained that his youngest daughter, Tabitha, was with him at the Capitol on Wednesday, Jan. 6. because it was the day after they buried her brother, his son, Tommy, "the saddest day of our lives," Raskin said.

"Also there was my son-in-law Hank, who's married to our oldest daughter Hannah, and I -- I consider him a son too, even though he eloped with my daughter and didn't tell us what they were going to do," Raskin joked, and got a laugh, before pivoting into his emotion-filled recollection of the rest of the day.

"The reason they came with me that Wednesday, Jan. 6, was because they wanted to be together with me in the middle of a devastating week for our family," he said. "They said they heard that President Trump was calling on his followers to come to Washington to protest and they asked me directly, 'Would it be safe? Would it be safe?' I told them, 'Of course it should be safe. This is the Capitol.'"

Raskin was separated from them for electoral business when rioters breached the building.

"And all around me people were calling their wives and their husbands, their loved ones to say goodbye. Members of Congress in the House were removing their congressional pins so they wouldn't be identified by the mob as they tried to escape the violence. Our new chaplain got up and said a prayer for us, and we were told to put our gas masks on," he said.

Raskin said the sound he'll never forget, the "most haunting sound I've ever heard" is one of "pounding on the door like a battering ram."

He said his staff, hiding, "thought they were going to die," and when he finally reunited when his daughter and son-in-law, a comment she made hit him, perhaps, hardest.

"I told her how sorry I was, and I promised her it would not be like this again the next time she came back to the Capitol with me. You know what she said? She said, 'Dad, I don't want to come back to the Capitol,'" Raskin said, fighting back tears. "Of all of the terrible, brutal things that I saw and that I heard on that day, and since then, that one hit me the hardest."

"That and watching someone use an American flag with the flag still on it, to spear and pummel one of our police officers ruthlessly, mercilessly tortured by a pole with flag on it that he was defending with his very life," he added, emphasizing the deaths and injuries from that day.

"We cannot have presidents inciting and mobilizing mob violence against our government and our institutions because they refuse to accept the will of the people under the Constitution of the United States. Much less can we create a new January exception in our precious, beloved constitution that prior generations have died for and fought for, so that corrupt presidents have several weeks to get away with whatever it is they want to do," he said to close his time.