(CNN) The Senate returns Monday. The House on Tuesday. The dynamics of impeachment are, from a practical standpoint, largely unchanged from where they were before the holidays . The array of questions from the most immediate: "when will the articles be transmitted to the Senate," to perhaps the most central: "will there be witnesses?" are still unanswered.

Bottom line: This is, finally, mercifully, the week questions start to get answered. Pay close attention to senators facing questions about what kind of trial they'd like to see play out. For months they've been able to dodge the question as the House moved through its inquiry and vote. That's no longer the case. It's time to put some positions on the record.

What to watch today: The full Senate returns to the Capitol for the first time in the new year, which will provide the first real opportunity to take the temperature of the rank-and-file members in weeks. Senate Majority Leader Mitch McConnell and his Democratic counterpart Sen. Chuck Schumer of New York will speak from the floor as well.

What about the House: The House doesn't return until Tuesday, and it remains unclear when the next time House Speaker Nancy Pelosi will speak, or take questions, will be at this point.

Good rule of thumb on the articles: There's a general expectation the articles will be transmitted this week among those in both chambers. But remember this: if Pelosi hasn't personally told you when she plans to send them over, you don't know. Period.

Will Iran change the impeachment calculation?

The early answer, according to lawmakers and aides in both chamber CNN spoke to over the weekend, is emphatically "no." One House Democrat made clear they are "separate issues" and the chamber has proven "we can do more than one thing at a time."

McConnell and Schumer have, to this point, kept them as completely separate issues, by design. There's no expectation that's going to change in the near-term, aides say.

A refresher on the key positions

Pelosi said before the holidays she wants to ensure what Democrats would view as a fair trial structure before sending over the articles of impeachment to the Senate. She's aligned with Schumer on the need for witnesses to be addressed up front. She also wants to know the structure before finalizing her impeachment managers.

said before the holidays she wants to ensure what Democrats would view as a fair trial structure before sending over the articles of impeachment to the Senate. She's aligned with Schumer on the need for witnesses to be addressed up front. She also wants to know the structure before finalizing her impeachment managers. McConnell has made clear his preference is to structure a trial where the House managers, then the President's defense team give presentations. Then senators can ask questions. Then they will either vote to subpoena witnesses or, if the votes aren't there for that, vote to acquit the President. McConnell has made clear he doesn't believe witnesses are necessary, and privately has noted they could very well work against Trump.

has made clear his preference is to structure a trial where the House managers, then the President's defense team give presentations. Then senators can ask questions. Then they will either vote to subpoena witnesses or, if the votes aren't there for that, vote to acquit the President. McConnell has made clear he doesn't believe witnesses are necessary, and privately has noted they could very well work against Trump. Schumer has been explicit that he wants subpoenas for four administration witnesses, and a raft of documents, included in any initial organizing resolution. All 47 senators who caucus with the Democrats support the position and each drip of news or information related to Ukraine has served, according to Schumer, to bolster his push to do so.

What happened last week?

McConnell reiterated his position on the Senate floor. Schumer did the same. Pelosi was mostly silent beyond a statement ripping into McConnell, saying he "made clear that he will feebly comply with President Trump's cover-up of his abuses of power and be an accomplice to that cover-up."

That was the extent of what Pelosi has said about impeachment in the last two weeks. So we wait.

How the Senate trial rules impasse ends: McConnell isn't going to move, according to people familiar with his thinking. If at least 51 of the 53 Senate Republicans back him in that position, he won't have to.

Reality check

At this point, there is no expectation a bipartisan agreement on the trial structure will be reached, according to people involved. That's what occurred in 1999 as it pertained to the first portion of the trial, but McConnell and Schumer are simply too far apart right now.

The most likely scenario is McConnell moves his own organizing resolution, along party lines, that sets up the first half of the trial.

The longer game: View everything Schumer is doing through lens of getting 51 votes on witnesses -- eventually. The witness proposal, the framing, the sharp and fast statements coming after any story that drips out new information about the Ukraine allegations -- it's all driving toward the idea that wary (or politically endangered) Republicans will have a choice to make: a robust trial with witnesses who have firsthand knowledge of events but declined to show up in the House, or stick behind McConnell.

Schumer has been making this point implicitly for weeks -- that four of Republicans essentially hold the keys to the trial structure in their hands. But he was explicit about it on ABC's "This Week." "I hope, pray, and believe there's a decent chance that four Republicans will join us. If they do, we'll have a fair trial."

To be clear, there haven't been any clear breaks in Republican ranks yet. But Democratic leaders, who are very much aligned now, are using every pre-trial moment they can to try and push them to that point.

Collins and Murkowski

What Collins and Murkowski (actually) said: Much attention was given to Republican Sens. Susan Collins of Maine and Lisa Murkowski of Alaska during the holidays, due to their remarks in local media interviews regarding where they stand on impeachment. And rightfully so: all eyes are on both, and both critiqued, either explicitly or implicitly, McConnell's stated close relationship and coordination with the White House on the trial.

But it's important to take a close look at what else the two moderates who are often swing votes said.

Murkowski didn't give an answer on whether she'd like to see witnesses and criticized House Democrats for not going through the courts to compel testimony. Collins said she was "open" to witnesses but that it was too soon to make that judgment.

Both appeared to pretty clearly line up with what McConnell has laid out as his preferred path, at least for the start of the trial -- presentations by the managers, then the defense, then questions from senators. Then decisions will be made (or votes will be had) on whether to subpoena witnesses.

This is a long way of saying, for all of the attention the comments got, neither broke with how McConnell wants to at least start this process. That obviously could change. But it hasn't yet.

When will the trial begin?

There is no good answer to this question right now beyond "we don't know." It's entirely contingent on Pelosi holding the vote to appoint managers and transmit the articles to the Senate. Pelosi hasn't tipped her hand as to when that may occur.

Even when it does, it's likely there will be several days of negotiations about how the trial will be structured before any real floor action kicks into gear.

In other words, this will be a process -- one in which without the first step, nothing else comes together.

Would McConnell consider starting a trial without the articles?

No. The answer is no.

The 1986 Senate rules related to impeachment state , in their first point, that the Senate acts only when it receives notice from the House that managers have been appointed and have been directed to transmit the articles to the Senate.

So in other words, a trial without the articles would require the chamber to essentially go around the standing impeachment rules, which would require 60 votes, or an explicit rule change which would require 67 votes. There are 53 Republican senators. They don't have the votes. Ostensibly the Senate could move to drop the threshold to a simple majority, but that would basically entail nuking the legislative filibuster.

It's more detailed and complicated than this, but that's a 30,000-foot way of looking at it, per people who have walked through this idea.

Here's the best way to summarize it: McConnell is not going to pursue this. Period.

What the Senate does if Pelosi continues to hold the articles: Conduct business as usual, particularly on the nominations front. McConnell said publicly on Friday he's just fine if the articles never come over and has already teed up nominations for this week for the Senate to move through in the absence of the articles.

And yet: That doesn't mean some in his conference won't do just that. Sen. Josh Hawley, a Missouri Republican, said he will introduce a motion on Monday to change the Senate impeachment rules to allow for a vote to dismiss the articles if they aren't sent over "for lack of prosecution."

It would come in a motion to update Senate impeachment rules, which would be subject to the much higher vote threshold. The votes for this don't exist, but it underscores the tension here.

Republican Sen. Lindsey Graham of South Carolina said on Fox News Sunday that if Pelosi doesn't send the articles over by the end of this week, the Senate should "take matters in our own hands" and change the rules to start the trial without the articles.

Just want to reiterate here once more: McConnell is not considering this, and the mechanics of doing it would, for lack of a better description, incinerate the Senate.

Your 'Who to Watch' Briefing

Republicans

The moderates:

Murkowski

Collins

There's no sense where either will end up, and that's not a new development. Both are very well-known to go through their own process (Collins was holding lengthy briefings with Congressional Research Service experts before the holidays) and McConnell gives both quite a bit of space to do just that. As one senior GOP aide put it to me before the holidays: "Jamming or whipping either of them is a fool's errand. They're going to do it their way, and we hope it comes out in our favor."

The 2020ers:

Sen. Cory Gardner of Colorado

Sen. Joni Ernst of Iowa

Sen. Thom Tillis of North Carolina

Sen. Martha McSally of Arizona

Collins

The natural place to look on a tough vote is to those who are running for reelection in swing (or swing-ish) states. Hence these five. There will certainly be a ton of pressure on them, along with ad money coming down in their states pushing them to go one way or another.

One thing to keep in mind here, however: in most, if not all, of the cases of these five senators, the political repercussions of voting against the President likely far outweigh the benefits. With a President as popular within the Republican Party as Trump is, raising his ire is an excellent way to potentially depress the base voters needed to make any of these races close, let alone tip them into the incumbents' direction.

Now, the caveat here is these decisions aren't always made through the purely political lens. And in a trial setting, there's a way to have it both ways (vote in favor of witnesses pushed by Democrats, but against removal). All of those things are possible and why these lawmakers are worth watching. But do keep in mind there isn't some clear political benefit to bucking the President just because they come from swing states.

The Romney:

Sen. Mitt Romney of Utah

Sen. Mitt Romney has repeatedly been willing to question or raise concerns about President Trump's actions, including as it relates to Ukraine. Yet he's also been careful not to commit to anything as it relates to the trial regarding what he'd like to see, as he continues to study past impeachments and the case itself.

The retirees:

Sen. Lamar Alexander of Tennessee

Sen. Pat Roberts of Kansas

Sen. Mike Enzi of Wyoming

The theory here is that one or more of these members may choose to side with Democrats at some point on voting to subpoena witnesses or documents on the grounds that a more fulsome trial is good for the institution they will soon be leaving. Of note: none of these senators have said anything publicly that would show they're willing to do that. Republican aides find it laughable that someone like Enzi or Roberts would break in any way from the party line, but Democrats have their eyes on all three -- Alexander in particular, who has taken great pains to keep his powder dry and not lean any way in advance of the trial.

Democrats:

Sen. Doug Jones of Alabama

Sen. Joe Manchin of West Virginia

Sen. Kyrsten Sinema of Arizona

All 47 senators who caucus with the Democrats support Schumer's push to have subpoenas for documents and witnesses in the initial organizing resolution (see Jones in The Washington Post ).

But beyond that, it's worth noting that there is no guarantee the entire Democratic caucus will vote to remove the President. Keep an eye on the three mentioned above. Jones makes clear in his op-ed he's not there yet, and unquestionably has the most difficult reelection race in the country. Manchin always takes his time on these types of votes and comes from a state that supports Trump in a major way. Sinema simply doesn't tip her hand, but has split with the broader caucus in the past. It's entirely possible there are Democrats who vote to acquit Trump, and these three are far and away the most likely candidates. But we just don't know yet.