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The Senate barreled toward a pivotal vote on whether to hear from witnesses in the impeachment trial of President Donald Trump on Wednesday with Republicans and Democrats both seeking an edge with the handful of undecided senators by grilling the House impeachment managers and the President’s lawyers.

After a week of sitting silently, senators finally got their chance to speak in the impeachment trial Wednesday by submitting questions to be read aloud by Chief Justice John Roberts directed at one or both of the legal teams.

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The back-and-forth questions – the two parties took turns asking them – presented an opportunities both for senators to try to shape the views of those on the fence as well as to provide some insight into the thinking of those key senators.

The first question was indicative of much the session was geared toward the undecideds. Senate Republicans gave the opening question of the day to Sens. Susan Collins of Maine, Lisa Murkowski of Alaska and Mitt Romney of Utah – the three Republicans seen as most likely to vote for witnesses.

Many of the questions asked Wednesday were friendly – Republicans teeing up talking points for the President’s legal team and Democrats doing the same for the House managers – but several questions would be considered hostile, such as when Republicans pressed House Intelligence Chairman Adam Schiff on the whistleblower or the Democrats questioned the President’s legal team about when they learned former national security adviser John Bolton’s book manuscript was sent to the White House.

Heads on the Senate floor perked up whenever one of the senators whose vote is being closely watched stood up to submit a question. They offered some hints about those senators’ thinking: Sen. Rob Portman of Ohio, a Republican Democrats have hoped to flip, asked the President’s team to discuss the implications for the Senate of moving forward with witnesses. Sen. Joe Manchin, a West Virginia Democrat, asked Trump’s lawyer Alan Dershowitz why his views on abuse of power and impeachment changed compared to what he said 20 years ago.

Senate Democrats seized upon another response from Dershowitz, the Harvard law professor emeritus on the President’s legal team, who argued that a quid pro quo to boost a president’s reelection chances cannot be impeachable because the politician is acting in the national interest.

The Senate is holding two days of questions for senators before it will debate on vote on seeking witnesses and documents in the trial. Senate Majority Leader Mitch McConnell told his conference on Tuesday Republicans didn’t currently have the votes to defeat the motion for witnesses, but Republicans left the meeting more confident they would ultimately be successful and end the trial without witnesses.

Most of the questions have been structured, as Democratic and Republican leadership have organized the questions submitted. But there’s the possibility for curveballs: GOP Sen. Rand Paul of Kentucky, a close ally of the President, wants to submit a question that would have named the alleged whistleblower, according to a source, and Roberts essentially said no to reading it aloud. Paul is upset at Republican leadership, another source said, since it was leadership who told him the chief justice wouldn’t read the name of the alleged whistleblower.

“It’s still an ongoing process — it may happen tomorrow,” Paul said during the dinner break on Wednesdasy evening.

But Sen. John Thune of South Dakota, the Senate’s No. 2 Republican, said that while lot of his members have questions about the whistleblower, “I suspect that (naming the whistleblower) won’t happen.”

Key senators listening in

The first question of the day gave a chance to look into the thinking of the Republican senators on the fence: Collins, Murkowski and Romney asked the President’s legal team how senators should consider if the President had multiple motives when he held up US security aid to Ukraine.

“If there is any possibility, if there is something that shows a possible public interest and the President could have that possible public interest motive — that destroys their case,” said Patrick Philbin, deputy counsel to the President. “So once you’re into mixed-motive land, it’s clear that their case fails.”

Senate Democrats teed up Schiff to respond on the next question — complete with videos of the defense counsel presentation to argue that the Senate should hear from Bolton.

“If you have any question about the President’s motivation, it makes it all the more essential to call the man who spoke directly with the President, that the President confided in and said he was holding up this aid because he wanted Ukraine to conduct these political investigations that would help in the next election,” Schiff said. “Don’t wait for the book.”

Later in the afternoon, Collins and Murkowski asked a question about whether the President had raised with his aides the issue of corruption in regards to Joe Biden and his son Hunter Biden before the former vice president entered the presidential race. Philbin said he didn’t know of specific conversations with Trump, saying he was limited by the House’s evidentiary record, and he discussed the investigative efforts of the President’s attorney Rudy Giuliani in Ukraine.

Later in the evening, Romney put a question to the President’s team about when the US aid was held up and what rationale the President gave at that point. Philbin said he could only rely on public information and what was in the House record.

The back-and-forth over Trump’s motives and Bolton kicked off two days of senator questions to the House managers and the President’s legal team, in the final phase of the trial before the Senate will debate and vote on whether to seek witnesses and documents. Senators still can’t speak during the trial, so they are written on a notecard and Roberts reads them aloud.

A copy of the question form used by senators on Wednesday.

When Philbin began answering a question from Portman about the implications for the Senate if they move forward on witnesses, Sen. Lamar Alexander of Tennessee began taking extensive notes. Philbin contended that such a step would set a dangerous precedent and paralyze the body.

Alexander, viewed by both sides as potentially the pivotal vote on witnesses, continued taking notes as Schiff made his counterpoint.

Senate leaders in both parties have worked with senators to craft questions that will be asked, as Republicans push for an end to the trial while Democrats make their case for calling witnesses and subpoenaing documents.

The vote on witnesses, which is expected Friday, comes down to the handful of Republicans who remain undecided on whether there should be witnesses called in the trial.

McConnell met on Wednesday morning with Murkowski, an Alaska Republican also on the fence about witnesses.

“I had a meeting with Leader McConnell, but I’m not going to talk to you about it,” Murkowski said after leaving McConnell’s office. “I am not going to be discussing the witness situation right now. … I’ve got some more questions that I want to get into the mix. So I’ve been talking with the folks in the cloakroom about what the universe is, see how we can supplement that, so that’s my purposes.”

Perhaps the biggest wildcard right now is Alexander, the retiring Tennessee Republican and Senate institutionalist who is close to members on both sides. He is also a McConnell confidant.

Sources who attended Tuesday’s Republican meeting say Alexander did not speak about his views on witnesses — and is not tipping his hand one way or the other. He is reading through the materials from the inquiry and past testimony and continues to say he will make a judgment after the questioning period is done.

On the Democratic side, there are still a handful of red-state senators who have not said how they will vote on whether to convict or impeach Trump on the articles of impeachment.

Manchin has said he wants witnesses, like Bolton. On Wednesday, Manchin said he was also potentially interested in a key witness sought by Republicans: former Vice President Joe Biden’s son, Hunter Biden.

“I want witnesses. I definitely want witnesses,” Manchin said. “The only thing I’ve said is that there should be an adult in the room and that’s Chief Justice Roberts. We should vote again on Chief Justice Roberts being able to determine who is pertinent … if Hunter Biden is one of the people who is pertinent to the evidence or to the trial, then absolutely.”

Questions to help make the case

At Wednesday’s session, the pace had changed from the often lengthy presentations that were delivered during opening arguments, as Roberts held each side to a five-minute response to the questions – cutting off those who went over their time.

Democrats spread out their questions to the House managers, with Schiff, the head manager taking the lead. Philbin answered a majority of the questions for the President’s team, with others chiming in occasionally.

Still, there were some notable responses, such as when Sen. Ted Cruz, a Texas Republican, asked the President’s team, “As a matter of law, does it matter if there was a quid pro quo?”

Dershowitz responded that a politician trying to win reelection is acting in the national interest, saying that Trump cannot be impeached for pressuring Ukraine for investigations into Joe Biden because the President’s motivations would ultimately be fueled by the public interest, if he believes his reelection is what’s best for the country.

“Every public official that I know believes that his election is in the public interest,” Dershowitz said. “And if a president did something that he believes will help him get elected, in the public interest, that cannot be the kind of quid pro quo that results in impeachment.”

Senate Minority Leader Chuck Schumer, a New York Democrat, asked Schiff to respond. “All quid pros are not the same,” Schiff said. “Some are legitimate and some are corrupt, and you don’t need to be a mind reader to figure out which is which.”

Occasionally, senators quizzed the lawyers on the other side of the aisle. Sen. John Kennedy, a Louisiana Republican, posed a question to both teams about why the House hadn’t challenged the President’s executive privilege claims. Sens. Lindsey Graham of South Carolina and Cruz asked the House managers a hypothetical about former President Barack Obama asking Russia for an investigation into his then-opponent, current Utah Sen. Mitt Romney.

Later, when asked about being invoked, Romney joked, “That’s not where you hope to be mentioned – is in an impeachment trial.”

Sen. Martin Heinrich, a New Mexico Democrat, asked the President’s team when the White House counsel had learned about the Bolton manuscript. Philbin said they had been notified of it, though he did not say when. And independent Sen. Angus King of Maine, who caucuses with the Democrats, asked both sides about former White House chief of staff John Kelly’s comments that he believes Bolton and he should testify. “Do you agree with General Kelly?” King asked.

Jay Sekulow, Trump’s personal lawyer, ticked off the denials from the President, the vice president and the Justice Department.

“To move that into a change in proceeding, so to speak, I think is not correct,” Sekulow said, adding that the President’s team expects witnesses if the House gets witnesses.

Schiff urged senators to hear from Bolton so they could judge for themselves.

“It’s really, at the end of the day, not whether I believe John Bolton, or whether General Kelly believes John Bolton,” Schiff said, “but whether you believe John Bolton – whether you’ll have an opportunity to hear directly from John Bolton, whether you’ll have an opportunity to evaluate his credibility for yourself.”

This story has been updated with additional developments Wednesday.

CNN’s Ted Barrett, Alex Rogers, Clare Foran, Maegan Vazquez, Allie Malloy and Nikki Carvajal contributed to this report.