The Senate chamber was particularly quiet as each senator’s name was called up to sign the impeachment trial “oath book.”

One exception was Sen. Bill Cassidy, R-La., who was having a robust conversation with Sen. David Perdue, R-Ga., as they sat together in the back of the chamber at their wooden desks.

All senators were present for this rare moment in history, except for GOP Sen. James Inhofe, who was in his home state of Oklahoma helping a family member with a medical issue.

CHIEF JUSTICE JOHN ROBERTS, SENATORS SWORN IN AS TRUMP IMPEACHMENT TRIAL OPENS

It wasn’t a typical day in the Senate. Chief Justice John Roberts was presiding. Senators had to take a special oath and were required to stay in their seats.

The press were subjected to additional access restrictions at the Capitol and required new press badges to be present. A special yellow ticket was also needed to enter the press gallery and watch Day One of the impeachment trial of President Trump.

Senators were banned from bringing electronic devices and cell phones to their seats. That left a unique situation for those in the gallery staring down at this fishbowl moment in history.

First, senators solemnly stood and raised their right hand and pledged “impartial justice” in the trial of the president. Afterward, the senators were called up to affirm their oath by signing their names.

As aides with clipboards ushered the senators to sign the "oath book," the vibe on either side of the Senate was different.

The Democrats seemed like astute students in the classroom ready to learn. Many had paperwork covering their wooden desks, notepads and pens out. Some were already jotting down notes.

On the GOP side, their wooden desks were largely bare. Some sat stiffly like they were prisoners to a process they believe shouldn’t be happening at all.

Sen. Cory Gardner, R-Colo., and Sen James Lankford, R-Okla., were GOP exceptions, and both were spotted taking notes.

At one point, Sen. Ted Cruz, R-Texas, was reading a book that a Cruz aide identified as the Constitution. Cassidy had a book on Senate procedures at his desk, open to the section on impeachment.

An aide later said Cassidy and Perdue were discussing the Prevent Government Shutdown Act and ways to reform the budgeting process. But largely senators only spoke in soft murmurs as they shared an exchange with their neighbor as the name-signing procession continued.

The biggest outfit stunner was Sen. Kyrsten Sinema, who wore a bright red v-neck cocktail dress with a cape. The Arizona Democrat channeled a superwoman vibe for the momentous occasion in a normally buttoned-up Capitol.

For such a big day in the Senate, attendance never reached capacity. Though not all sections are open to the public, there were roughly a couple hundred seats vacant. One notable guest in the senators' family section was Jane Sanders, wife of Sen. Bernie Sanders, I-Vt.

For his part, Sanders sat with a pen in hand ready to take notes at the trial opening. When it was his turn to sign the oath book, he greeted Sen. Ben Sasse, R-Neb., with a handshake.

All the 2020 White House hopefuls left their campaigns to be jurors.

Sen. Elizabeth Warren, D-Mass., walked so quickly and purposefully to sign the oath book, that she almost collided with Sen. Mark Warner, D-Va., when he stopped in front of her in line. Sen. Amy Klobuchar, a moderate who has preached on the presidential campaign trail about her ability to work in a bipartisan fashion, made a beeline for the GOP side of the aisle after the Senate trial adjourned. She had a conversation with Sen. Roy Blunt, R-Mo., the chairman of the Senate Rules Committee.

Klobuchar, a daughter of a journalist, earlier this week expressed concerns about the severe press restrictions during impeachment and said she had raised the issue with Blunt.

Sen. Susan Collins, R-Maine, and Sen. Lisa Murkowski, R-Alaska, sat next to each other without notes or paperwork on their desks. The two moderates are often partners when they break with their party on some thorny issues. Democrats are counting on them to be the two of the four senators they need to vote in favor of allowing witnesses and documents into the trial.

Collins said Thursday she's inclined to support a motion to call witnesses after the first phase of the trial is complete.

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The Senate trial adjourned until Tuesday. Senate Democrats told reporters afterward they hoped the solemnity and gravity of the occasion would shake loose some more Republican votes over the weekend.

“We should have a trial -- not a cover-up -- that features documents, evidence (and) witnesses, rather than a historic sham that fails to meet the moment,” Sen. Chris Coons, D-Del., said.