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(CNN) The second day of questions in President Donald Trump's impeachment trial began -- and ended -- with some drama and some clarity.

The drama involved Kentucky Sen. Rand Paul, Supreme Court Chief Justice John Roberts and the whistleblower whose complaint last August set this entire process in motion. Roberts refused to read Paul's question because it named the alleged whistleblower. Watch that moment here.

That's a big deal since Roberts read every other question, including one from Elizabeth Warren in which he had to ask about the "loss of legitimacy of the Chief Justice, the Supreme Court and the Constitution."

Here's our main report from Capitol Hill , which chronicles how the whistleblower was the subject of several dustups.

Republicans are poised to unite behind the President to spare him the damaging testimony of his former national security adviser John Bolton, whose book manuscript leaked at the start of the week just as Trump's legal team was beginning its defense.

If it was not clear before, it is more and more clear now: This is Donald Trump's GOP and the senators are not about to vote against their political interests.

Here are seven key questions that still need to be answered.

When will this end?

Trump could be acquitted by close of business Friday. That leaves three days, give or take a few hours, before the 2020 caucuses begin in Iowa, where Trump is on the Republican ballot.

On the podcast: I got the latest from CNN's Jeremy Herb and talked about how all of this will affect 2020 with CNN political commentator Amanda Carpenter on the Daily DC Impeachment Watch. Listen here.

Before that, though, what happens if there's a 50-50 tie on calling witnesses?

We have just published a story on this very topic. Read it here

Senate math

Sen. Susan Collins of Maine late Thursday night became the first Republican to support calling witnesses, as expected. But while all eyes had been on Sen. Lamar Alexander of Tennessee, he announced shortly thereafter that he would not be the fourth Republican Democrats need to win a vote on calling witnesses. Assuming Sens. Mitt Romney and Lisa Murkowski do vote for witnesses, that means a 50-50 tie could result.

Tie-breaks

Normally, the vice president breaks ties in most matters in the Senate. But it's not expected that Mike Pence -- who was in Iowa on Thursday -- would be called in to an impeachment trial. During the impeachment trial of President Andrew Johnson, it fell to Salmon Chase, the chief justice at the time, to break two ties. Read all about Johnson's trial here.

Letting it lie

But it's not thought by senators on both sides of the aisle that Roberts would follow the Chase precedent. Rather, the expectation is that he would allow a question that results in a 50-50 tie to fail. But we'd just have to wait and see. He could surprise us. Democrats have suggested simply giving him the power to decide whether witnesses are relevant, but Republicans, who are in the majority, seem unlikely to go along with that idea.

Last gasp

Democrats are still pushing the idea that witnesses can be moved quickly through the trial. Rep. Adam Schiff suggested a one-week period for depositions and a "limited" time for witnesses, pushing back on concerns of "endless" delays. He said the chief justice can deal with any disputes. "This can be done very quickly."

Will any Democrats vote to acquit Trump?

So much time has been spent on the more immediate question of whether Republicans would vote for hearing from witnesses, or reject it to spare Trump damaging testimony from Bolton, that we're just coming to focus more directly on the ultimate vote.

It is possible that Trump's acquittal could be bipartisan if any of a handful of moderate Democrats who represent states Trump won in 2016 -- Sens. Joe Manchin of West Virginia, Kyrsten Sinema of Arizona, Gary Peters of Michigan and Doug Jones of Alabama -- break with their party.

And remember, there are two articles of impeachment, so these senators could vote to remove Trump on the first article -- abuse of power -- and to acquit him on the second -- obstruction of Congress.

"Everyone is going to make their own decisions," Senate Minority Leader Chuck Schumer told CNN when asked if he would push his caucus to vote the party-line on conviction. "But we have great unity in our caucus."

Is an acquittal vindication for Trump?

House Speaker Nancy Pelosi was asked about the near certainty that Trump is acquitted. She demurred.

"Well, he will not be acquitted," she told reporters. "You cannot be acquitted if you don't have a trial. And you don't have a trial if you don't have witnesses and documentation."

This is going to be the key political question going forward. Democrats felt they couldn't not impeach Trump after he tried to use Ukraine to taint former Vice President Joe Biden with unfounded and false claims

But they were also never likely to actually remove him from office. He'll beat his chest about being acquitted by the Senate, if that happens Friday or Saturday. But he'll also always be the third impeached President, after Johnson and Bill Clinton.

What else will we learn?

We have learned so many things since the House vote in December, and we'll probably continue to learn so many new things about Trump and Ukraine.

A new video was released Thursday of Trump interacting with Lev Parnas , the indicted former associate of Trump lawyer Rudy Giuliani who has made serious allegations against the President concerning what happened in Ukraine.

John Bolton's book , eventually, will come out. Even if Republicans collectively decide they don't want to hear the former national security adviser talk about Trump's effort to condition military aid on political favors, that story will likely be published before Election Day.

Documents from the Pentagon and State Department will eventually be released. Officials involved in Ukraine at the White House will, someday, tell their side, whether under oath or to the press.

All of this will happen after Trump is acquitted by Republicans.

How will this change the US system of government?

Trump's lawyers claimed sweeping executive power for him as they argued for his acquittal. Alan Dershowitz implied that no President up for reelection can abuse power by working for his own reelection -- even though he tried to walk back that argument later on Thursday, it's certainly true that Trump has viewed Congress as an impediment to be squashed or worked around rather than a coequal branch of government.

How Trump, stained by impeachment but emboldened by acquittal, works with Congress now that they've gone to the brink will be an important relationship for every American to watch. It's notable that, during his Senate impeachment trial, he signed the new USMCA trade deal into law . He couldn't have done that without Nancy Pelosi's support. At the same time that on Thursday the House passed resolutions to curb his power to wage war . But he's likely to test the Constitution when he sees fit in the future.

Will Republicans move on from the whistleblower?

While it's an open question whether outing the whistleblower breaks the law , it's also clear Trump's Justice Department isn't going to pursue anyone who does it. The Paul/Roberts episode shows both that there is still an appetite among Republicans to pursue retribution against the whistleblower and, perhaps, others involved both in revealing Trump's secret Ukraine policy and also his impeachment.

The whistleblower and his or her identity figured prominently Thursday as the President's attorney, Jay Sekulow, argued, despite the law, that whistleblowers aren't entitled to anonymity -- while Schiff vehemently chastised anyone who would try to out the whistleblower.

What's next