WASHINGTON — Pennsylvania Republican Sen. Pat Toomey sent the strongest signal yet that he won’t support calling witnesses in President Donald Trump’s impeachment trial, saying Wednesday he was “very, very skeptical” any witness could change how he would ultimately vote on Trump’s political fate.

“As I’ve said from the beginning, my decision about a witness is going to be whether or not there is a fact in dispute that a witness can shed enough light on that it could resolve the dispute, and do so in a way that would change my mind about how I ought to vote on the final question," Toomey said. "And I’m very, very skeptical ... that that criteria is going to be met.”

Toomey’s stand on one of the only major questions left in the trial leaves Democrats with dwindling options when it comes to persuading Republicans to agree to call witnesses who might shed additional light on Trump’s conduct with Ukraine. Democrats need support from at least four GOP senators to subpoena additional witnesses and documents, including John Bolton, the former Trump national security adviser who has reportedly written in a forthcoming book that the president was personally involved in a scheme to withhold military aid in order to pressure Ukraine to investigate Democrat Joe Biden.

Bolton, who has said he would testify if subpoenaed, could be the first witness with firsthand information to directly link Trump to the plot. The revelation about his book has rocked the impeachment trial after weeks of Republican resistance to calling witnesses.

“Look, the public’s going to hear it. They’re going to read a book,” Toomey said when asked if there’s a public interest in having the former Trump aide testify under oath. “I expect that he’s going to be doing a tremendous amount of media interviews. I think there’s going to be a lot of information out there. The job before us is not to entertain, you know, all kinds of possible discussions about this. It’s to evaluate the articles of impeachment that have been brought over by the House.”

Toomey spoke to The Inquirer and the Morning Call of Allentown on Wednesday morning, the day after opening arguments in the impeachment trial concluded and as Republicans began to truly confront the question of whether any of them would vote to call witnesses. A vote on the issue is expected as soon as Friday, after senators spend Wednesday and Thursday posing questions to impeachment managers and the White House defense team.

Without witnesses, a final vote on impeachment could occur Saturday.

Toomey’s vote against Trump’s removal appears virtually certain. He said Wednesday that Democrats presented a “very weak case, a very badly flawed case,” and that “I have not yet seen even the allegation of an act that rises to the level of impeachment.”

Toomey’s comments came one day after sources close to Senate Majority Leader Mitch McConnell (R., Ky.) told reporters that Republicans don’t yet have enough votes to block witnesses, a clear sign to those wavering to make their intentions known.

Toomey, who won reelection in 2016 by vowing to be “an independent voice” in the Senate and has criticized some of Trump’s behavior and policies, largely echoed the White House and GOP arguments on this issue, including by raising questions about Hunter Biden, son of former Vice President Joe Biden.

Democrats this week have escalated their insistence that Bolton be called to testify. The New York Times reported Sunday that Bolton wrote that Trump personally told him he was withholding $391 million in military aid to Ukraine unless the country began an investigation into the Bidens, confirming the central accusation in the impeachment charges.

Republicans are “tying themselves in all kinds of pretzel knots to avoid the truth,” Senate Minority Leader Chuck Schumer (D., N.Y.) said Wednesday.

He accused the GOP of prioritizing Trump’s acquittal above seeking more information. “Talk about being political. Talk about being cynical. ... We, the Senate, Democrats and Republicans, have an obligation to seek the truth. A fair trial matters, whatever the outcome.”

Toomey said that if witnesses are called, it would only be fair for both parties to have the opportunity to call them, and that the GOP would almost certainly seek to hear from Joe or Hunter Biden. He said Hunter Biden would be important because his past position on the board of the Ukrainian energy company Burisma offers another explanation for why Trump might have withheld aid.

“The House managers have rested a tremendous amount of their case on the notion that President Trump could not possibly have had any motive whatsoever for asking for an investigation into Burisma and the Bidens except his corrupt personal political motive,” Toomey said. “But when you look at the facts involving Hunter Biden and Burisma, it’s begging for an investigation about corruption.”

He noted that Hunter Biden, with few qualifications, landed a lucrative seat on the board of the energy company while his father was vice president and spearheading policy toward Ukraine.

Democrats have scoffed at the notion that Trump was concerned about nepotism or corruption, noting that Trump only raised alarms about Burisma once Joe Biden entered the 2020 presidential race. Trump also pressured Ukraine to investigate a debunked conspiracy theory about 2016 election interference.

Joe Biden, as vice president, led a push to oust a Ukrainian prosecutor while his son sat on the energy company’s board. But Biden was carrying out the official policy of the United States and its European allies in trying to oust a prosecutor noted for being soft on corruption. Hunter Biden was not accused of any wrongdoing, and the investigation into Burisma was dormant at the time.

Sen. Bob Menendez (D., N.J.) said that despite Hunter Biden’s Burisma job, the Trump administration approved 45 installments of aid to Ukraine worth $1.5 billion until June 2019, a few months after Joe Biden became a presidential candidate.

“Hunter Biden is irrelevant and a distraction,” Schumer said.

One Democrat, the moderate Sen. Joe Manchin of West Virginia, who has partnered with Toomey in the past in pushing gun control legislation, said Wednesday morning on MSNBC that Hunter Biden would be a relevant witness to call.

Earlier this week, Toomey had reportedly floated a proposal with Republican colleagues that would essentially amount to a witness trade, in which each party would get to call one witness. Democrats sharply criticized that idea on Tuesday.

Toomey said that he was not advocating for additional witnesses, only saying that if there were any called, both parties should do so.