Senators brace for contentious Tuesday as impeachment trial begins in earnest

Democrats will try to amend the organizing resolution that will be offered by Senate Majority Leader Mitch McConnell. Under McConnell's plan, there is expected to be no guarantee that there will be witness testimony or documents produced, decisions Republicans want to punt until after opening arguments are completed on both sides and senators have a chance to ask questions.

But Democrats will attempt to change that. Senate Minority Leader Chuck Schumer is expected to offer at least one amendment to stipulate that witnesses must testify and that documents blocked so far by the White House be turned over to senators. But Democratic senators told CNN that it's possible Schumer could try to offer multiple amendments, and that could stretch debate on for several more hours.

That's because, at the moment, it's expected that there will be two hours of debate -- equally divided between the two parties -- for each amendment.

It's still uncertain how many amendments there would be, or precisely how Tuesday's debate would shake out because McConnell has yet to unveil his resolution publicly that will detail the procedures of the trial.

Opening arguments from the House Democratic managers would not occur until after debate over the amendments concludes and the Senate resolution is adopted. GOP senators are expected to unify and reject the Democratic amendments.

Here's where things could also get interesting. Senators are not allowed to debate in open session while the trial is ongoing. If they want to debate, they would have to go into closed session, and a vote of at least 51 senators is required to make the proceedings private.

Otherwise, the amendments would be debated in public between the House impeachment managers and President Donald Trump's defense team.

Schumer on Thursday suggested he would seek to limit the number of closed sessions that would occur.

"I would like it to be as open -- I mean, might there be an occasional moment where we think we might come together in a closed session? Yes, but the strong presumption is to be open, and I want to see as much of it open as possible," Schumer told reporters.

A Senate leadership aide said that closed sessions might be needed since senators are required to keep quiet during an impeachment trial.

"Closed-session deliberations are a common feature because it's the only time when the Senate's impeachment rules permit senators to talk," the aide said. "Outside of closed session, senators have to be silent. So any time the members want to deliberate and discuss a resolution or a motion in the chamber, closed session is their only option."