Some House lawmakers, fresh off votes across the Capitol, arrived on the floor of the Senate chamber to watch the proceedings.
Representatives Dean Phillips of Minnesota and Tom Malinowski of New Jersey, both Democratic freshmen, could be seen standing by the doors behind the Republican desks.
When a staff member gently pointed them to the Democratic side of the aisle, they walked over and sat down behind the Democratic desks.
Before the questioning could begin, Representative Jason Crow, Democrat of Colorado and a freshman colleague, walked over to chat quietly with them.
On the Republican side, Representatives Chip Roy and Daniel Crenshaw, both of Texas, came in the opening moments of the trial, joining Representative Alex X. Mooney of West Virginia in the back of the room.
Representative Adam B. Schiff of California, the lead House manager, wasted little time on Thursday hammering away at the remarkably expansive view of presidential power put forward by President Trump’s defense team the night before.
“What we have seen over the last couple days is a descent into constitutional madness,” Mr. Schiff warned senators in response to a friendly question from Senator Jon Tester, Democrat of Montana.
The manager said that arguments put forward by Alan M. Dershowitz, one of Mr. Trump’s lawyers, and other members of the president’s defense team essentially boiled down to the famous phrase from former President Richard M. Nixon: “If the president does it, it’s not illegal.” Even Republican senators had expressed some discomfort at the logic after Wednesday’s session, and Mr. Schiff sought to highlight Mr. Dershowitz’s most provocative statements.
“They compounded the dangerous arguments that they made that no quid pro quo is too corrupt if it helps your election campaign by saying, and if what you want is targeting your rival, it’s even more legitimate,” Mr. Schiff said. “That way, madness lies.”
Mr. Dershowitz said on Thursday that his comments had been mischaracterized. He said he did not intend to say that a president could do anything as long as he “believes that his re-election was in the national interest.”
Mr. Dershowitz continued to defend himself on Twitter after the trial began, challenging his critics to a “Lincoln/Douglas-type town hall debate in which name calling is prohibited and intellectual arguments must be responded to with other intellectual arguments.”
After failing to get Chief Justice John G. Roberts Jr. to read the name of the person widely thought to be the whistle-blower whose complaint prompted the impeachment inquiry into President Trump, Senator Rand Paul, Republican of Kentucky, did so himself on Thursday.
Mr. Paul, who left the Senate chamber while the impeachment trial was in session to hold a news conference about Mr. Roberts’s refusal to read his question, said it “deserved to be asked.” He said the question had nothing to do with the whistle-blower, then he proceeded to read it aloud and name the person.
The question asked whether House impeachment managers or the president’s legal defense team were aware of reports that two individuals “may have worked together to plot impeaching the president before there were formal House impeachment proceedings.”
He also posted the question verbatim on Twitter.
At the news conference Mr. Paul asserted that the two had been “working together for years looking for an opportunity” to impeach the president.
Mr. Paul defended himself for asking the question, saying it “made no reference to any whistle-blower or any kind of person, a complaint from the whistle-blower.”
“I think it was an incorrect finding not to allow the question,” he told reporters.
The Kentucky Republican’s disclosure of the name of the person believed to be the whistle-blower on Thursday was not the first time that he has done so. He has repeatedly urged media organizations to reveal the person’s name and in at least one interview with a Washington D.C. radio station, he said it himself.
Senator Marsha Blackburn, Republican of Tennessee, on Thursday defended the president’s lawyer, Alan M. Dershowitz, who faced an onslaught of criticism after making this argument on Wednesday: “If the president does something that he thinks will help him get elected, in the public interest, that cannot be the kind of quid pro quo that results in impeachment.”
“He was talking about rooting out corruption and fighting corruption,” Ms. Blackburn said Thursday on CNN. “And then that is in the public interest.”
Ms. Blackburn added, “waste, fraud and abuse,” and went on to say that this was at the root of Mr. Trump’s comments to President Volodymyr Zelensky of Ukraine.
Earlier in the day, Mr. Dershowitz asserted that his statements were misconstrued by the news media.
Democratic senators have promised to question Mr. Dershowitz about it on Thursday during the remaining time for senators’ questions. Ms. Blackburn has been an avid defender of Mr. Trump’s through the entire Ukraine matter.
Chief Justice John G. Roberts refused on Thursday to read aloud a question submitted by Senator Rand Paul of Kentucky that would have named a person widely believed to be the C.I.A. whistle-blower in the Ukraine affair.
“The presiding officer declines to read the question as submitted,” Chief Justice Roberts said after Mr. Paul submitted the question during President Trump’s impeachment trial.
On Wednesday, Mr. Paul repeatedly sought to submit the question, but it was not sent to be read aloud by the chief justice. Just before Mr. Paul sent his question to the desk on Friday, Senator Mitch McConnell of Kentucky, the majority leader, made comments that appeared to be directed at discouraging Mr. Paul’s actions.
“We’ve been respectful of the Chief Justice’s unique position in reading our questions,,” Mr. McConnell said. “And I want to be able to continue to assure him that that level of consideration for him will continue.”
Mr. Paul described the rejected question on Twitter.
Republican leaders said they are increasingly confident that the Senate will turn back the Democratic effort to extend the impeachment trial with new witnesses and documents in a Friday vote.
Senator Roy Blunt of Missouri, a top Republican leader, said Thursday: “We are getting to where we need to be on the witness vote.”
Senator John Barrasso of Wyoming, the No. 3 Republican in the Senate, said his party is pressing to conclude the third impeachment trial in the nation’s history, though he expected Democrats to use procedural gimmicks to try to prevent it.
“The goal would be to get this done tomorrow evening,” Senator John Barrasso of Wyoming, the No. 3 Republican in the Senate, told reporters before the second question period in the trial began. “I don’t know if Chuck Schumer has opportunities to try to slow down the process, but I don’t think we end up leaving the Senate floor, leaving the chamber, until it’s done.”
A four-hour debate on whether to seek additional witnesses and documents is expected to take place Friday, and Democrats need the support of at least four Republican senators. Several Republican leaders predicted that their party would prevail in blocking the Democratic effort.
Senator Lindsey Graham, Republican of South Carolina, said that he is “getting more optimistic” that they will reject the demand for witnesses and move to a quick conclusion to the trial. He praised Senator Mitch McConnell of Kentucky, the Republican leader.
“He’s pretty good at what he does, and I’ve been in the room where people are beginning to consolidate,” Mr. Graham said.
Even so, rank-and-file Republican senators emerging from a private luncheon said the leadership was not certain they had the 51 votes necessary to block witnesses.
“We don’t know for sure,” Senator Mike Braun, Republican of Indiana.
Senator Chuck Schumer, the minority leader, suggested Thursday that Democrats would use parliamentary procedures to thwart Republicans’ plans for a speedy acquittal of President Trump.
“The minority has rights, and we will exercise those rights,” Mr. Schumer told reporters, without elaborating.
The trial’s organizing resolution, written by Senator Mitch McConnell, the majority leader, and adopted along party lines, specifies that once the question-and-answer portion of the trial is finished, the Senate will vote on whether to call witnesses.
But the resolution is not specific about what happens after that vote, Mr. Schumer said. Democrats need the votes of four Republicans to expand the scope of the trial to include witnesses; if they fall short, as seems increasingly likely, Mr. Schumer hinted they would make some other move to prevent immediate votes on whether to convict or acquit.
But he refused to tip his hand.
“We’re not going to get into that here,” he said. “Our focus right now is on getting the four.”
Senator Rand Paul, Republican of Kentucky, will insist on Thursday that Chief Justice John G. Roberts Jr. read aloud his question on the origins of the impeachment inquiry, a day after the question was repeatedly rejected because it would name the C.I.A. whistle-blower who first raised concerns about President Trump’s actions toward Ukraine.
Republicans and Democrats have expressed deep reservations about Mr. Paul’s efforts to out the whistle-blower. But in a statement, Mr. Paul said he would insist that his question be read at the beginning of Thursday’s impeachment trial session.
“Senator Paul believes it is crucial the American people get the full story on what started the Democrats’ push to impeach President Donald Trump, as reports have indicated Obama appointees at the National Security Council may have discussed organizing an impeachment process in advance of the whistle-blower complaint,” Mr. Paul’s office said in the statement.
Senator Lindsey Graham, Republican of South Carolina, said Thursday morning that he did not believe the identity of the whistle-blower should be revealed by Mr. Paul in a question on the Senate floor.
“Not in this environment,” he told reporters, though he added that “later on we need to look at it.”
Asked about his plans Thursday morning, Mr. Paul said only: “We have a question, that’ll be at 1 o’clock, and you’ll find out about it.” He declined to answer any other questions about his intentions.
Speaker Nancy Pelosi of California said on Thursday that regardless of the outcome of his impeachment trial, if the Senate refuses to call new witnesses or subpoena more documents, President Trump’s acquittal will not be legitimate.
“He will not be acquitted,” Ms. Pelosi told reporters at her weekly news conference, when asked whether the president is likely to be chastened or emboldened by the all but certain verdict in his favor, which could come as early as Friday.
“You cannot be acquitted if you don’t have a trial,” she added. “You don’t have a trial if you don’t have witnesses and documentation and all of that,” she said.
Her comments came the day before an expected Senate vote on whether to summon additional witnesses for the impeachment trial, as Republican leaders appear to be lining up the votes to block the move.
“The fate of our nation is riding on how this is resolved,” Ms. Pelosi said. “It isn’t about just one person. It’s about the precedent that it sets for the future.”
In this case, she said, it was also a matter that demanded urgent action by the Senate, given the allegations against Mr. Trump that he sought to invite foreign meddling in the 2020 election on his own behalf and ample evidence that Russia is trying to interfere again, as it did in 2016
“The Russians are coming, the Russians are coming,” Ms. Pelosi warned. “And the president has led a clear path for them to interfere, once again, in our elections, as they are currently doing.”
“I just pray that the senators will have the courage, and the ability, to handle the truth,” she added.
It was not the first bid by Ms. Pelosi to ensure that regardless of the outcome of the Senate trial, the public does not see an acquittal as an exoneration.
“This president is impeached for life, regardless of any gamesmanship on the part of Mitch McConnell,” she told ABC News this month. “He will be impeached forever.”
Nothing would please President Trump more than to have a bipartisan acquittal in his impeachment trial. He just might get his wish.
While attention has focused on the handful of Republicans who might break ranks, cracks are beginning to show in Democrats’ unity. Senator Doug Jones, facing a tough re-election in Alabama, has hinted he might vote to acquit Mr. Trump of at least one charge, obstruction of Congress.
And two other centrist swing state Democrats — Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona — are also being eyed as possible defectors.
Ms. Sinema is a wild card; she issued a statement when the trial began saying she was taking her obligation seriously — and has said nothing public since. When Mr. Trump’s legal team wrapped up its defense earlier this week, she remained on the Senate floor, deep in conversation with Senator Lamar Alexander, Republican of Tennessee and a close ally of Senator Mitch McConnell, the majority leader.
Mr. Manchin has complained about what he has called the “hypocrisy” of both Mr. McConnell and Senator Chuck Schumer, the Democratic leader. When President Bill Clinton was impeached, both men took positions opposite to the ones they are taking now. Like Ms. Sinema, he has given little hint how he will vote. But he has sided with Republicans in saying that Hunter Biden, the son of the former Vice President, might be a relevant witness.
Mr. Jones is unlikely to acquit Mr. Trump on the first charge, abuse of power. He suggested Wednesday that he might vote to acquit Mr. Trump on the charge of obstruction of Congress, though he said that the president’s own behavior was strengthening the case against him.
“I’m still looking at that very closely; there are some things that trouble me about it,” Mr. Jones said, without elaborating. “But I will tell you this about the obstruction charge: The more I see the president of the United States attacking witnesses, the stronger that case gets.”
Democrats are expected to question Alan Dershowitz, one of Mr. Trump’s lawyers, a day after he argued that the president can do whatever he must to get re-elected, because that is in the public’s interest.
“If the president does something that he thinks will help him get elected, in the public interest, that cannot be the kind of quid pro quo that results in impeachment,” Mr. Dershowitz said on Tuesday, prompting some jaws to drop in the Senate chamber.
On Thursday, Mr. Dershowitz said in a tweet that his comment is being mischaracterized.
Senator Brian Schatz, Democrat of Hawaii, said in a tweet that Mr. Dershowitz should come prepared to explain himself during the second full day of questions at the impeachment trial.
“It is essential that you clarify this on the Senate Floor, not on this website,” Mr. Schatz tweeted in reply to Mr. Dershowitz’s tweet denying his expansive presidential powers argument.
“We haven’t met, but I was one of the Senators with my mouth agape as I heard it.”
Senator Richard Blumenthal, Democrat of Connecticut, said that when he and other colleagues walked off the Senate floor they turned to each other and said, “Did he really say that? It prompted laughs, but also a deep anger,” Mr. Blumenthal said Thursday on CNN, adding that he and the other senators went to check the transcript to be sure.
Mr. Blumenthal added, “It would be laughed out of a courtroom.”
Hillary Clinton, who ran against Mr. Trump in 2016, offered her thoughts, as well.
“Richard Nixon once made this argument: ‘When the president does it, that means that it is not illegal.’ He was forced to resign in disgrace. In America, no one is above the law,” she wrote in a tweet.
On the other side of the Capitol, the House later this morning will take aim at President Trump’s ability to authorize future military action against Iran without the assent of Congress, imposing yet another constitutional check on Mr. Trump even as the Senate weighs whether to remove him.
The House will vote on two measures: one to repeal a 2002 resolution authorizing military force that the administration initially used to justify the strike that killed Maj. Gen. Qassim Suleimani, Iran’s top security commander, and on another that would bar Mr. Trump from using federal funds for an unauthorized strike against Iran.
The 2002 authorization of military force, passed by Congress to defend against the perceived threat posed by Saddam Hussein’s regime, has long been eyed warily by Democrats and an increasing number of libertarian-minded Republicans, who argue it is now outdated and serves only to provide the president cover to move forward with new, unauthorized strikes.
The White House has threatened to veto both measures, arguing they would infringe on Mr. Trump’s ability to protect American forces and strip him of the constitutional powers afforded to him as the commander-in-chief.
Senator Mitch McConnell, Republican of Kentucky and the majority leader, is not expected to take up the bills in the Senate.
Alan Dershowitz, who defended President Trump on Wednesday by asserting an expansive view of presidential power in which presidents can do virtually anything in pursuit of their re-election, claimed on Thursday that his arguments had been mischaracterized.
Answering a question from Senator Ted Cruz, Republican of Texas, about quid pro quos, Mr. Dershowitz forcefully insisted that if a president believes his re-election is in the national interest, then the things he does in pursuit of it is not impeachable.
“Every public official that I know believes that his election is in the public interest,” Mr. Dershowitz, a celebrity defense attorney and member of Mr. Trump’s legal team, said on the floor of the Senate.
He added: “And if a president does something which he believes will help him get elected, in the public interest, that cannot be the kind of quid pro quo that results in impeachment.”
The argument stunned many in the chamber, who saw it as effectively excusing anything Mr. Trump did to further his chances of staying in office. Democratic senators called it “absurd” and “wrong,” while even some Republican distanced themselves from his arguments.
“They characterized my argument as if I had said that if a president believes that his re-election was in the national interest, he can do anything,” Mr. Dershowitz wrote on Twitter. “I said nothing like that, as anyone who actually heard what I said can attest.”
Mr. Dershowitz complained that the media did not accurately report his remarks. “Taking advantage of the fact most of their viewers didn’t actually hear the senate Q and A, CNN, MSNBC and some other media willfully distorted my answers,” he wrote.
President Trump will visit two battleground states Thursday as his defense team and House managers begin a second day of answering questions from senators in his impeachment trial.
Mr. Trump will visit Michigan, where he will highlight the signing of the U.S.M.C.A. trade agreement, one of his key legislative accomplishments during his time in office. Then, he will head to Iowa for a campaign rally, just four days before the caucuses in the state, where Democrats will begin the first votes toward choosing their eventual nominee.
In the split-screen that has been a hallmark of Mr. Trump’s time in the White House, he will be carrying out official activities and then taking part in campaign events, as official Washington is focused on a debate over his conduct in office.
Senator Rand Paul, Republican of Kentucky, was prevented from asking a question on Wednesday because the question he posed, in relation to the origins of the impeachment inquiry, would have named the whistle-blower, according to a person familiar with the situation.
“It’s still an ongoing process; it may happen tomorrow,” Mr. Paul told reporters on Wednesday.
But at least one member of Senate leadership said that he did not believe that the whistle-blower, whose complaint sparked the impeachment inquiry, would be named on the Senate floor.
“I don’t think that happens, and I guess I would hope that it doesn’t,” said Senator John Thune, the No. 2 Republican in the chamber.
The still-anonymous whistle-blower filed a complaint last summer, after President Trump’s July 25 call with Ukraine’s president. The complaint was filed through an official process meant to protect those filing from reprisals.
Much of the focus will again be on the chamber’s few moderates and the queries they choose to pose during the remaining eight hours of questioning. On Wednesday, Senator Susan Collins, Republican of Maine, was given the first question, which she chose to ask in tandem with Senators Lisa Murkowski of Alaska and Mitt Romney of Utah, both Republicans.
The three senators are seen as the most likely Republicans to vote for witnesses, and their colleagues in the chamber seemed to perk up every time one of the three submitted a question.
“Some of them were good,” Ms. Murkowski said of the nearly 100 answers she heard on Wednesday.
The chamber will also focus on three centrist Democrats: Senators Joe Manchin III of West Virginia, Doug Jones of Alabama and Kyrsten Sinema of Arizona.
Ms. Sinema, holding a question card, could be seen Wednesday night conferring with her colleagues in the back of the chamber over possible questions to ask.
All the Democrats and at least four Republicans would have to support hearing witnesses to reach the 51 votes needed.
As a growing chorus of Republican senators declared on Wednesday that they felt ready to move to a final vote without calling new witnesses, the president’s legal team delivered several bold answers to senators’ questions. Among the most remarkable was an argument from Alan M. Dershowitz, who suggested that anything President Trump might have done in the service of his own re-election effort was in the public interest.
The president’s lawyers seemed increasingly self-assured in a stance others have offered before: Regardless of whether the Democrats’ impeachment allegations are true, the president’s actions still would not justify his removal from office.
Even as the 16-hour period of questioning comes to a close on Thursday, both sides will still have an opportunity to deliver something akin to a closing argument as early as Friday. But as the president’s lawyers sense that the trial could move toward a swift conclusion, they may elect to commit to the notion Mr. Dershowitz offered on Wednesday that any more discussion, and any testimony from new witnesses, should be considered irrelevant.
Senator Chuck Schumer of New York, the minority leader, expressed doubts on Wednesday that he would be able to secure the votes to introduce new witnesses in the trial. At the same time, Democratic and Republic senators alike began tailoring their questions to effectively turn the members of each legal team into witnesses themselves.
Representative Adam B. Schiff, the chairman of the House Intelligence Committee and lead impeachment manager, was asked about what he and his staff knew about the C.I.A. official who filed a whistle-blower complaint that prompted the impeachment proceedings, and how that information informed the committee’s investigation. Democrats indicated that they hoped to press Pat A. Cipollone, the White House counsel who is leading Mr. Trump’s defense team, for details about his experience in the White House specific to the case against the president.
On Thursday, senators may look to home in what outstanding information still exists. Several people like John R. Bolton, the former national security adviser, and Lev Parnas, an associate of the president’s personal lawyer Rudolph W. Giuliani’s who helped pressure Ukraine to investigate Mr. Trump’s political rivals, indicated this week that they would be willing to testify if subpoenaed. Bracing for an outcome in which those in Mr. Trump’s orbit never appear, senators may look for creative ways to discuss what those potential witnesses could have added to their case.
What we’re expecting to see: The trial will reconvene for a final day of questioning, as senators submit written questions for House impeachment managers and White House lawyers. Chief Justice John G. Roberts Jr. will again read the questions aloud and hold responses to five minutes.
When we’re likely to see it: The proceedings will begin at 1 p.m. Eastern and could run for about eight hours, or until senators feel they have exhausted their lines of questioning.
How to follow it: The New York Times’s congressional and White House teams will be following all of the developments and will be streaming the trial live on this page. Stay with us.