Senators used their second and final day of questioning in the impeachment trial of President Donald Trump to tee up debate on whether to subpoena documents and witnesses that did not appear during the House’s impeachment inquiry. The late night announcement that Tennessee Republican Sen. Lamar Alexander will vote against additional witnesses Friday signals that there likely won’t be enough votes to continue the trial much longer.

After senators exhausted their cumulative 16 hour question and answer session with House managers and Trump’s lawyers, Alexander, who will retire at the end of his term, announced that on Friday he will vote against hearing from new witnesses.

“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. 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,” Alexander said in a statement.

“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. I believe that the Constitution provides that the people should make that decision in the presidential election that begins in Iowa on Monday,” Alexander continued.

With all eyes on moderates, Republicans and Democrats who reside in the middle took the chance Thursday to dig into remaining uncertainties they had about the case before the critical vote Friday. Alexander, a retiring moderate and institutionalist, had been mum on the issue until now.

Among the most scrutinized senators, Maine Republican Susan Collins was first out of the gate after the chamber adjourned to announce she would vote to consider witnesses. “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. Therefore, I will vote in support of the motion to allow witnesses and documents to be subpoenaed,” she said in a statement. 

Democrats contend that the Senate must obtain documents from the White House Office of Management and Budget and hear from former Trump officials like John Bolton. Trump’s foes contend those documents and witnesses can undisputedly prove that Trump temporarily withheld $391 million in military aid intended for Ukraine in hopes that Kyiv would announce an embarrassing investigation into Trump’s potential 2020 opponent, former Vice President Joe Biden.

At the conclusion of the proscribed 16 hours of the question and answer period, the Senate will move Friday to debate whether to subpoena witnesses or introduce new documents. Democrats have been advocating for additional witnesses for weeks, while Republican leadership and Trump’s defense team argue no additional information should be introduced to the case.

It will take four Senate Republicans to join all Democrats to get a majority vote to allow witnesses and documents and keep the trial going. Absent that, a majority of senators could vote against the introduction of new information. That will inevitably lead to an end to the trial, which would conclude with votes to acquit or convict the president.

With all eyes on moderates, Republicans and Democrats who reside in the middle took the chance to dig into remaining uncertainties they had about the case before critical votes on Friday.

The most pointed question came more than seven hours into questioning when Alaska Republican Lisa Murkowski asked Trump’s lawyers why the Senate should not call Bolton to testify when there are competing reports on whether Trump sought a political favor in exchange for military aid. Bolton’s coming memoir reportedly says that Trump did exactly what Democrats allege. In her query, Murkowski said the dispute about material facts “weighs in favor” of calling material witnesses.

Later, again in primetime, West Virginia Democrat Joe Manchin III asked why the Senate shouldn’t “slow down” after Trump’s counsel and other Republicans argued that the House rushed its impeachment proceedings.

Alexander, a retiring moderate who might vote to hear more witnesses, asked his first question late Thursday that cast doubt on that possibility.

The question, which was joined by Republican Sens. Ted Cruz of Texas and Steve Daines of Montana, asked House managers to compare the bipartisanship in the Nixon, Clinton and Trump proceedings.

“Specifically, how bipartisan was the vote in the House of Representatives to authorize and direct the House committees to begin formal impeachment inquiries for each of the three presidents?” the Alexander question said.

The senators certainly already knew what Trump’s lawyers would later clarify: That 31 Democrats joined Republicans in the Clinton inquiry, and no Republicans joined Democrats to authorize the Trump investigation.

Murkowski joined Hawaii Democrat Brian Schatz to ask “where’s the line between permissible political actions and impeachable political actions?” Throughout the trial, Trump’s defense team has argued that elected officials often make policy decisions with their next election in mind. The House managers, though, assert that Trump’s alleged scheme had no policy implications.

Earlier, Collins led a group of four fellow Republicans to ask both sides whether there were any “legitimate” reasons a president could ask a foreign government to “investigate a U.S. citizen, including a political rival, who is not under investigation by the U.S. government?”

Alabama Democrat Doug Jones, who is facing a tough 2020 reelection campaign in a state that Trump won handily in 2016, asked the House managers what authority substantiated the subpoenas issued by House members before the House officially voted to start their impeachment inquiry. The White House’s refusal to cooperate with congressional subpoenas is at the heart of the second article of impeachment.

Manchin, Schatz and New York Democrat Kirsten Gillibrand asked the managers and Trump’s counsel if they had ever been involved in a trial in which they were unable to call witnesses or submit evidence. Schatz and Gillibrand will surely vote to hear from additional witnesses, but Manchin has sided with Republicans before on consequential votes, like when he broke with his party to support the confirmation of Supreme Court Justice Brett Kavanaugh.

Late Thursday, Collins, and Republican Sens. Marco Rubio of Florida and Jim Risch of Idaho asked the House managers why they withdrew their subpoena for former deputy national security adviser Charles Kupperman during the impeachment inquiry. Trump allies have argued throughout the trial that the House fast-tracked Trump’s impeachment for their own political purposes and now want the Senate to conduct the investigatory work that the House neglected.

Lead impeachment manager Adam B. Schiff rebutted arguments from Republicans that calling witnesses would prolong the trial, suggesting a limited one-week timeframe for depositions.

He pointed to the one week deposition period used during the 1999 Clinton impeachment trial and said the Senate could resume its regular legislative business while depositions were conducted.

“Is that too much to ask in the name of fairness — that we follow the Clinton model, that we take one week?” he asked. “Are we really driven by the timing of the State of the Union, should that be a guiding principle? Can’t we take one week to hear from these witnesses?”

“I think we can,” Mr. Schiff concluded. “I think we should. I think we must.”

Schiff’s comments on the floor echoed what Minority Leader Charles E. Schumer told reporters Wednesday. He said that when he pushed to hear from witnesses at the beginning of the trial, Republicans said to wait until after the arguments, but now are saying there is not time for witnesses.

“We could get the whole thing done a week,” said Schumer.

Todd Ruger contributed to this report.