Washington (CNN) Television networks and cable channels have gone gavel-to-gavel this week on coverage of the Senate impeachment trial of President Donald Trump, airing every word from every speaker into the middle of the night.

But what viewers are seeing is not the full picture. The cameras and video feeds distributed to the public are controlled by the US Senate -- the very institution hearing the case -- and are solely focused on who is speaking, with no shots of the rest of the chamber.

There have been few to no shots of reaction from lawmakers or the opposition legal team or views of the entire chamber to see if the 100 senators are even at their desks and listening to the evidence.

The limits may be having a tangible political impact on how the public is perceiving the trial. If senators of one party or another aren't paying attention or are reacting a certain way, it could sway how Americans feel about whether the Senate should convict the President.

"Ironically, the senators themselves are the jury -- they are the judges. You don't see their reaction, you don't see them sleeping, you don't see the ones who aren't there," said Princeton professor and CNN political analyst Julian Zelizer.

"The last thing Republicans want right now is for a camera to pan the chamber to show a bunch of the senators aren't there," Zelizer added. "That would be problematic and politically embarrassing."

And eyes will be on Democratic senators once Trump's legal team begins presenting its rebuttal arguments. Presidential contenders Sens. Amy Klobuchar of Minnesota, Bernie Sanders of Vermont, Elizabeth Warren of Massachusetts and Michael Bennet of Colorado are also at the trial.

Many people familiar with House and Senate debates from C-SPAN may not be surprised that this is how the system has worked for decades, and only in the big moments such as this does it draw attention.

For the impeachment trial, C-SPAN asked to install its own cameras, a request joined by CNN, ABC, CBS, Fox and NBC. The networks also asked to obtain independent feeds from all cameras, so they would be allowed to choose the pictures that would be broadcast. The requests were not granted.

Before the House and Senate allowed cameras on the floor, only high-profile hearings on issues such as Watergate or organized crime were broadcast. "It was seen as a potentially dangerous thing," Zelizer said. "They didn't want to embarrass people who were not paying attention. They didn't want to reveal that most of the time members weren't there."

When cameras were allowed, they became a potent political weapon. In the 1980s and early 1990s, congressmen such as Republican Rep. Newt Gingrich of Georgia -- later the House speaker -- would give speeches criticizing Democrats meant only for the TV cameras. There would be few people in the chamber, and since lawmakers could speak on any subject, it seemed as if there were no answers from the other side.

Then-House Speaker Tip O'Neill eventually ordered the cameras to show the full empty chamber and chastised Gingrich, setting off a partisan fight that helped elevate Gingrich and humiliated the Democratic speaker.

What you see

The camera angles for Trump's impeachment trial have been fairly simple and are determined by the Senate. When a House manager or attorney for the President is giving a presentation at the lectern on the Senate floor, there's a close-up shot of the speaker.

When Majority Leader Mitch McConnell or Minority Leader Chuck Schumer speaks, the cameras turn that way. When it's Chief Justice John Roberts ' turn, we can see the multi-tiered Senate dais. Only when there has been a roll call vote, such as those Tuesday on blocking Democratic amendments, has a full picture of the room finally been broadcast.

The limits have been amplified by strongly enforced prohibitions against bringing electronic devices and cameras into the chamber (there's a magnetometer at the entrance to the press gallery). Journalists from all news organizations are sending reporters in and out of the chamber to describe what they see -- but even that's not being transmitted in real time.

"With the Senate in control of what images are broadcast and disseminated, the public loses that right to independent access and are left reliant on what the government wishes them to see and hear," said Mickey Osterreicher, general counsel of the National Press Photographers Association. "This is something we as a democracy strongly object to when done by other countries."

McConnell's office did not immediately respond to a request for comment on the camera rules.

Aside from the limited TV views, only sketch artists have been able to give glimpses of what the Senate won't let people see. And while journalists may be familiar with how things look, most people are not, adding to the curiosity in this historic moment.

Sketch artist Bill Hennessy , speaking on CNN Thursday morning, described the mood overall as "pretty serious" and "fairly tense" -- but senators have gotten restless as the trial has progressed.

Near the end of House Intelligence Chairman Adam Schiff's opening arguments Wednesday, Hennessy said, many seats were empty and some lawmakers were either standing behind their desks or walking around, "and then it seemed a lot of them wandered out."

Schumer, meanwhile, suggested that everything was well-received. "The atmosphere of the Senate took on an entirely different dimension," he told reporters Thursday morning.

Either way, without cameras, people are "missing the full effect of how Schiff is being received," Zelizer said.

A contrast with other historic moments

This all is in contrast to other historic moments in the Capitol.

At the annual State of the Union address and other presidential speeches in the House chamber, on the other side of the Capitol, TV networks have been allowed to bring in their own cameras to capture the reactions of lawmakers. This is done via a pool system to limit crowding in the room, but the cameras are nevertheless controlled by journalists.

As a result, Americans are familiar with scenes of lawmakers from a president's party giving rousing standing ovations to parts of his speech, contrasted with the opposition sitting on their hands or fiddling with their phones.

Meanwhile, in this partisan and fractured media atmosphere, what viewers aren't seeing in the chamber may be viewed as an editorial decision by networks, Zelizer said.

"If people get upset about the way this is covered, it will be natural in 2020 that they assume this is what the networks are doing; whereas it's just the rules of Congress that governs what can happen."