Before senators could get started on the charge against former President Donald J. Trump, they spent the afternoon on Tuesday debating whether they had the right to try a former president in the first place.
Here are five takeaways from the first day.
Senators decided that a former president can, indeed, stand trial for impeachment.
In a 56-to-44 vote, the Senate rejected the argument from Mr. Trump’s defense team, and decided along mostly party lines that it had the jurisdiction to try an impeached former president. This paved the way for the trial to proceed on Wednesday.
Only a simple majority was required, unlike the two-thirds majority needed for a conviction. Six Republicans joined all 50 Democrats in deciding that the Senate could proceed with the trial.
Democrats, led by Raskin, promised compelling video footage of the events of Jan. 6, and they delivered.
In a 13-minute video of scenes from the Jan. 6 assault on the Capitol, the lead House impeachment manager, Representative Jamie Raskin of Maryland presented a graphic visual record of the attack, including rioters’ explicit language and rally cries, as well as clips of Mr. Trump’s comments during the day — like his speech to supporters before some of them stormed the Capitol and a Twitter post, hours after the attacks, in which he wrote, “Remember this day forever.”
The scenes of chaos in the video showed a mob of protesters violently pushing past security barricades, and footage from inside the building included an officer screaming as he was being crushed by a door. The footage delivered different vantage points from that day than what many of the senators experienced firsthand, as they were rushed out of the very same Senate chamber in shock and fear.
The expected outcome of this Senate trial is the same as Mr. Trump’s first.
The Democrats would need 17 Republicans to break with the former president and vote with them to have the two-thirds necessary to convict Mr. Trump. If the six Republican senators who voted with Democrats on Tuesday also vote to convict Mr. Trump, Democrats would still need the support of 11 more Republicans to secure a conviction.
Senator Patrick Leahy, Democrat of Vermont, is a witness, a juror and the judge.
As the longest serving Democrat in the Senate, Mr. Leahy, 80, is the presiding officer in the Senate’s trial of Mr. Trump. Chief Justice John G. Roberts Jr. and Vice President Kamala Harris declined to assume the role, and because the Constitution does not stipulate who should oversee the trial of a former president, it fell to Mr. Leahy, giving him the authority to rule on key questions like what evidence is admissible.
On Jan. 6, Mr. Leahy was among the lawmakers who had to rush away from the violent mob, making him one of hundreds of witnesses to the attack. And as one of 100 senators, he will also vote on whether to convict Mr. Trump of inciting violence against the United States.
The first lawyer to speak in Mr. Trump’s defense left senators a bit confused about his team’s strategy.
Bruce L. Castor Jr., the lawyer who began the Trump defense team’s arguments on Tuesday, took senators down a winding path of generalizations about the Senate, Mr. Trump’s right to free speech and the difference between murder and manslaughter in the criminal justice system.
“I have no idea what he’s doing,” Alan M. Dershowitz, who served on Mr. Trump’s defense team during his first impeachment trial last year, said on the conservative television station Newsmax. “Maybe he’ll bring it home, but right now, it does not appear to me to be effective advocacy.”
And after the proceedings ended, Senator John Cornyn, Republican of Texas, told reporters: “The president’s lawyer just rambled on and on. I’ve seen a lot of lawyers and a lot of arguments, and that was not one of the finest I’ve seen.”