WASHINGTON — Senator Lamar Alexander, Republican of Tennessee, said late Thursday that although he believed that Democrats had proved their case that President Trump acted “inappropriately” in his dealings with Ukraine, he did not think the president’s actions were impeachable and would vote against considering new evidence in the impeachment trial.
Mr. Alexander’s statement was a strong indication that Republicans had lined up the votes to block a call for more witnesses and documents on Friday and press toward a quick acquittal in the third presidential impeachment trial in history. His opposition was a significant victory for the White House and Republican leaders.
“The question then is not whether the president did it, but whether the United States Senate or the American people should decide what to do about what he did,” Mr. Alexander said in a late-night statement after the conclusion of a second marathon day of questioning by senators. “I believe that the Constitution provides that the people should make that decision in the presidential election that begins in Iowa on Monday.”
In announcing his stance, Mr. Alexander effectively conceded that the president had engaged in a corrupt effort to leverage taxpayer money to advance his own political objectives — the basis of the abuse-of-power charge against him — but said he had concluded such actions were not impeachable. He called the second charge, obstruction of Congress, “frivolous.”
“It was inappropriate for the president to ask a foreign leader to investigate his political opponent and to withhold United States aid to encourage that investigation,” he said in a statement released at 11 p.m. “When elected officials inappropriately interfere with such investigations, it undermines the principle of equal justice under the law. But the Constitution does not give the Senate the power to remove the president from office and ban him from this year’s ballot simply for actions that are inappropriate.”
His announcement capped a day of intense lobbying both on the floor of the Senate and off as each side sought to appeal to a shrinking group of undecided Republicans. Shortly before Mr. Alexander declared his intentions, Senator Susan Collins of Maine, another moderate, became the second Republican to say definitively that she would vote in favor of considering new evidence, after Senator Mitt Romney of Utah.
Democrats would need four Republicans to join them in voting for a motion to consider additional witnesses and documentary requests. After Mr. Alexander and Ms. Collins made their positions clear on Thursday night, all eyes turned to a fourth possible Republican swing vote, Senator Lisa Murkowski of Alaska, who said she would announce her decision on Friday.
Both parties deemed it nearly impossible that any other Republican senator would defect.
As the trial neared a critical turning point, both parties were already looking beyond the verdict and framing their arguments to voters ahead of the November elections.
“If the American people decide that they don’t like what’s happened here, that they don’t like the constitutional violations that have happened, that they don’t like the attack on a successful president for purely partisan political purposes, then they can do something about it, and they can throw them out,” said Pat A. Cipollone, the White House counsel.
Bracing for a likely defeat of their efforts to force witnesses to be heard at the trial, Democrats forecast what is likely to be their message after the verdict is reached, asserting that Mr. Trump’s acquittal would be illegitimate because the trial was flawed.
“He will not be acquitted,” Speaker Nancy Pelosi, Democrat of California, told reporters at her weekly news conference. “You cannot be acquitted if you don’t have a trial. You don’t have a trial if you don’t have witnesses and documentation.”
Even before Mr. Alexander announced his stance on witnesses, Senate Republican leaders projected confidence that they would line up the requisite votes, and privately plotted the trial’s endgame. Senator Mitch McConnell, Republican of Kentucky and the majority leader, spent much of Thursday toiling behind the scenes to cajole wavering moderates and stifle any move to prolong the trial by admitting additional evidence.
Asked about the looming vote as he arrived on Thursday morning to the Capitol, he told reporters: “I’m always confident.”
Ms. Murkowski appeared to be grappling with her position on Thursday evening. After the Senate broke for dinner, she submitted a question for Mr. Trump’s defense team asking why the Senate should not hear from John R. Bolton, his former national security adviser, who wrote in an unpublished book that Mr. Trump said he would not release the military aid for Ukraine until the country assisted in investigations of his political rivals.
She noted that account, reported on Sunday by The New York Times, contradicted Mr. Trump’s explicit denials that he had linked the military aid and investigations.
“This dispute about material facts weighs in favor of calling additional witnesses with direct knowledge,” Ms. Murkowski asked. “Why should this body not call Ambassador Bolton?”
But later, she joined with Mr. Alexander and other senators in asking Mr. Trump’s team if they agreed that even if Mr. Bolton’s account were true, the president’s conduct did not rise to the level of an impeachable offense. They did.
The House Democratic prosecutors made their final pleas to call the former national security adviser as the vote drew closer.
“The truth is staring us in the eyes,” said Representative Adam B. Schiff of California, the lead House manager. “We know why they don’t want John Bolton to testify: It’s not because we don’t know what really happened here, they just don’t want the American people to hear it in all its ugly, graphic detail.”
Mr. Alexander, a former education secretary and presidential candidate set to retire at the end of the year, met privately with Ms. Murkowski earlier Thursday evening when the trial broke for dinner and also informed Mr. McConnell of his decision.
He then returned to the floor and read a copy of “Impeachment: An American History” and hand-drafted a statement announcing a decision that even his staff did not yet know.
Mr. Alexander’s final statement made clear that he would vote to acquit Mr. Trump, as well, even if he did not condone his conduct.
“If this shallow, hurried and wholly partisan impeachment were to succeed, it would rip the country apart, pouring gasoline on the fire of cultural divisions that already exist,” he said.
Ms. Collins gave far less insight into her thinking on the underlying charges, but said that she saw value in hearing more.
“I believe hearing from certain witnesses would give each side the opportunity to more fully and fairly make their case, resolve any ambiguities, and provide additional clarity,” she said in a statement released just before Mr. Alexander’s. “Therefore, I will vote in support of the motion to allow witnesses and documents to be subpoenaed.”
Earlier inside the Senate chamber, the usually scripted trial got off to a tense start on Thursday when Senator Rand Paul, Republican of Kentucky, submitted a question that included the name of a person widely believed to be the C.I.A. whistle-blower whose anonymous complaint about Ukraine helped prompt the impeachment inquiry.
After studying the question card, Chief Justice John G. Roberts Jr. refused to read it aloud, instead saying, “The presiding officer declines to read the question as submitted.”
An indignant Mr. Paul then rushed out of the chamber straight to waiting television cameras to read the question aloud himself. He asked if the prosecution and defense teams were aware of reports that two government officials “may have worked together to plot impeaching the president before there were formal House impeachment proceedings.”
Mr. Paul’s move reflected how Mr. Trump’s conservative allies have sought to turn the tables on the entire inquiry, shifting the focus away from the president’s conduct and toward what they suggest was a conspiracy by his opponents to manufacture a basis for removing him.
The theme has been a favorite of the president’s, and is all but certain to figure prominently in his re-election campaign after his acquittal as he makes the case to voters that the impeachment effort was an affront to them as much as a challenge to him.
In a rare bipartisan question — one of only three out of more than 170 submitted — Ms. Murkowski and Senator Brian Schatz, Democrat of Hawaii, asked that given the actions of any president are to some extent inherently political, how should senators distinguish between permissible political actions and impeachable ones.
Patrick Philbin, a deputy White House counsel, said trying to discern a politician’s motive “is very dangerous.”
“There is always some eye to the next election,” he said, “and it ends up becoming a standard so malleable that in reality really is a substitute for a policy difference: If we don’t like a policy difference, we attribute it to a bad motive.”
Mr. Schiff countered that impeachment was the appropriate “political punishment for a political crime” involving corrupt activity.
“If we go down that road” of ignoring a corrupt motive, Mr. Schiff said, “there is no limit to what this or any other president can do.”
The vote on Friday does not deal directly with individual witnesses or sets of documents. Rather, it will resolve whether the trial should even consider calling additional witnesses and evidence.
If a majority of senators vote no, Republican leaders could move the proceeding to final deliberations and a speedy up or down vote on each article of impeachment, possibly as early as Friday. If they vote yes, the trial would blow open and could become a free-for-all in which any group of 51 senators could band together to issue subpoenas for testimony and records of their choosing.
But senators in both parties were also bracing for the distinct possibility that the witness and documents vote could end in a 50-50 tie. Such an outcome would put Chief Justice Roberts in a difficult position. There is precedent, drawn from the 1868 impeachment trial of President Andrew Johnson, of a chief justice casting a tiebreaking vote on a procedural motion. But despite Democratic hopes, Chief Justice Roberts is unlikely to want entangle himself in a dispute that has been so thoroughly politicized.
If the chief justice abstained from breaking a tie, the motion would fail.
Michael D. Shear, Sheryl Gay Stolberg and Catie Edmondson contributed reporting.