The impeachment trial of President Donald Trump formally started with the swearing in of Chief Justice John Roberts and the Senate.

“Do you solemnly swear that in all things appertaining to the trial of the impeachment of Donald John Trump, president of the United States, now pending, you will do impartial justice according to the Constitution and laws, so help you God,” Roberts said to the senators, all standing at their desks.

“I do,” they responded.

The chamber was largely silent as senators, called one by one, signed a document affirming their oath as jurors. Some lawmakers, like Sen. Tim Scott (R-SC) and Sen. Rob Portman (R-OH), whispered to one another, while Sen. Bill Cassidy (R-LA) said something to Sen. Ben Sasse (R-NE) that made him smile and chuckle. Sen. Krysten Sinema (D-AZ) was the most stylish, in a red flowing dress with a cape.

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Most senators tried to project an air of seriousness at the moment, a piece of political theater that many viewers have never seen, given the last impeachment trial took place 21 years ago.

“When the Chief Justice walked in, you could feel the weight of the moment. I saw members on both sides of the aisle visibly gulp,” Senate Minority Leader Chuck Schumer (D-NY) told reporters.

They included four running for president: Sen. Amy Klobuchar (D-MN), Sen. Bernie Sanders (I-VT), Sen. Elizabeth Warren (D-MA) and Sen. Michael Bennet (D-CO). All will have to be present for the trial rather than on the campaign trail.

For his part, Trump tweeted later in the afternoon, “I JUST GOT IMPEACHED FOR MAKING A PERFECT PHONE CALL!”

I JUST GOT IMPEACHED FOR MAKING A PERFECT PHONE CALL! — Donald J. Trump (@realDonaldTrump) January 16, 2020

It’s unlikely that 2/3 of the Senate will vote to convict Trump, the threshold for his removal from office, but news anchors still stressed the historic nature of the occasion, which has only occurred twice before.

Fox News Sunday‘s Chris Wallace told viewers, “You couldn’t escape as you saw the Chief Justice there delivering the oath, the gravity of this moment. Whether you think this is just what should be happening or it’s the last thing that should be happening, this is a deadly serious matter now. These are hundred Senators considering the future of the country, considering the future of the Trump presidency. There’s a gravity to it, it’s right there in the Constitution, and it’s going to be fascinating to watch how it plays out, and I don’t think we are entirely certain how it will play out.”

The trial is scheduled to begin in earnest at 1 PM ET on Tuesday.

Democrats are pressing for the trial to include new fact witnesses and documents. Schumer already has requested that former National Security Adviser John Bolton, Acting Chief of Staff Mick Mulvaney, Mulvaney adviser Robert Blair and Office of Management and Budget official Michael Duffey be called. Schumer didn’t rule out requesting Lev Parnas, the former associate of Trump’s personal lawyer Rudy Giuliani, who has provided documents to the House and gave a revealing interview to Rachel Maddow on Wednesday.

But Senate Majority Leader Mitch McConnell has refused to commit to calling witnesses, raising the prospect that the Senate jurors will vote on the issue. Schumer said that he expects that on Tuesday.

Immediately after the swearing in, some members of the press tried to gather comment from exiting lawmakers, but at points they were told by Capitol Police to gather behind a velvet rope in a reception area, as Senate leadership put in place more restrictive measures during the trial. Few senators jumped at the chance to talk to the media. One of the few, Sen. Tom Carper (D-DE), said that he was “struck by the sense of gravity” of the moment in the chamber.

The restrictions also apply to the members of the Senate. Its sergeant at arms, Michael Stenger, announced to the chamber, “All persons are commanded to keep silent, on pain of imprisonment.” In other words, watch even when you whisper.

PREVIOUSLY, 10:46 AM: Reporters are complaining about restrictions that have been placed on their reporting on Capitol Hill as impeachment proceedings take place.

Capitol Police have a much greater presence in the hallways along the Senate chamber, as journalists are staked out to interview lawmakers. But some groused that authorities were interrupting interviews.

Alex Daugherty, a reporter for the Miami Herald, wrote on Twitter that he was interviewing Sen. Marco Rubio (R-FL) when police made him stop.

“Was just blocked by Capitol police from continuing an interview with @marcorubio on Puerto Rico aid. He wanted to talk, but the insane rules in place on the press for the impeachment trial prevented me from asking another question.

He added, “To be clear, this isn’t a criticism of the police, who are doing their jobs, it’s a criticism against the Senate rule makers who’ve decided that impeachment merits cutting off access to elected officials.”

The Standing Committee of Correspondents, a group of reporters that oversees the press gallery operations and its credentialing, has complained to Senate Majority Leader Mitch McConnell and Senate Minority Leader Chuck Schumer about the rules being put in place. Among other things, reporters are being restricted to a rope line in areas off the Senate chamber, making it more difficult to catch lawmakers as they enter and exit the proceedings.

CBS News even obtained flashcards that are being given to senators with tips on how to avoid reporters.

JUST IN: @CBSNews /@caitlinconant obtain a flashcard being given to U.S. Senators ahead of the #ImpeachmentTrial on tips to avoid reporters. (One thing it doesn’t suggest is calling reporters a “liberal hack.”) pic.twitter.com/mAZpBP9Fv7 — Ed O'Keefe (@edokeefe) January 16, 2020

PREVIOUSLY, 9:37 AM PT: Rep. Adam Schiff (D-CA) read the articles of impeachment against President Donald Trump in the Senate on Thursday, signaling the formal start of the impeachment trial later this afternoon.

Schiff, the lead House impeachment manager, walked in another procession through the Capitol along with the six other House managers and the House sergeant at arms to the Senate chamber. Schiff soon after took to a lectern to read the lengthy articles, which charge Trump will abuse of power and obstruction of Congress.

In a somewhat slow pace and careful tone, Schiff recited the House’s resolution, lasting for about 10 minutes. He said, “Wherefore, President Trump, by such conduct, has demonstrated that he will remain a threat to national security and the Constitution if he allowed to remain in office, and has acted in a manner grossly incompatible to self governance and the rule of law.”

“Very formal, very solemn,” NBC News anchor Lester Holt said after the proceedings.

CBS and NBC interrupted daytime programming for coverage of the proceedings, while ABC covered on ABC News Live, its streaming channel. All of the networks are planning special reports when the trial begins in earnest next week.

Later on Thursday, Chief Justice John Roberts will be escorted by four senators into the chamber, and then will be sworn in as the presiding judge for the proceedings. Then, the senators will be sworn in as impeachment jurors. But the trial won’t start in earnest until Tuesday, with the expectation that it will last at least two weeks.

The ceremonial nature of the proceedings were unusual, as commentators tried to explain why the articles had to be formally walked through the Capitol twice.

On Wednesday evening, networks also covered the same House impeachment managers as they made their way past the Capitol’s ornate hallways and statutes to the doors of the Senate. Wednesday’s delivery was merely to give notice that the House had impeached Trump. With Thursday’s delivery, the Senate was prepared to hear the actual articles.