WASHINGTON — There’s not much suspense in the impeachment trial of President Donald Trump, with his acquittal by the Republican-controlled Senate all but assured. But on one of the few major questions left, Sen. Pat Toomey is holding his cards close to the vest.

The Pennsylvania Republican has neither supported Democrats’ calls for new witnesses nor completely slammed the door on the possibility.

While Toomey votes with Trump and Republican Senate leadership about 90% of the time, his stand leaves the senator as one of only a handful of lawmakers yet to commit on the issue of calling witnesses. And it could make him a sought-after vote as the trial unfolds in the coming days.

The vast majority of senators, including Toomey, appear certain to vote along party lines when it comes to Trump’s conviction or acquittal. One of the few unknowns in the trial is whether lawmakers and the public will hear from new witnesses, such as the president’s former national security adviser John Bolton.

Three GOP senators have expressed openness to hearing from witnesses, like Bolton and other current and former White House officials. Those witnesses might have firsthand information about the Trump administration’s effort to pressure Ukraine to investigate Joe and Hunter Biden, and how directly the president was involved. Senate Democrats, if they stick together, need four Republicans to cross the aisle to have a majority vote in favor of witnesses.

Toomey hasn’t given much indication that he would support the idea. Overall, he has expressed serious doubts about the charges against Trump, strongly signaling he will vote to acquit the president.

“The Senate should conduct a fair trial consistent with past precedent," Toomey said in a statement last week as senators were sworn in as jurors. "We will allow House managers to make their case, the President’s lawyers to make their defense, and senators to pose questions. At the conclusion of these presentations, the Senate can then decide what, if any, further steps are necessary.”

He reiterated that view Thursday but added that he sees a significant potential downside in the long legal fight that might ensue if the Senate calls witnesses and Trump attempts to use executive privilege to block them.

“Calling witnesses could prolong this enormously, not just a couple weeks, it could be months,” Toomey told Lilly Broadcasting, bringing the trial even closer to a November election when voters will decide Trump’s political fate.

Toomey also stuck to his position that he hasn’t seen any evidence yet that rises to the level of removing a president from office. “That’s a very, very high bar,” he said.

Toomey’s stand on witnesses is in keeping with how he often deliberates and keeps his final intentions private until shortly before politically contentious votes. History shows that Toomey, like most GOP lawmakers, typically ends up siding with Republican leadership, with a few notable exceptions. Recently, for example, Toomey was the only Republican senator to oppose Trump’s new trade deal with Mexico and Canada.

Over the course of the Trump presidency, liberals have fumed at GOP senators who have hinted at breaking with the president only to eventually vote with him.

“I’ll believe it when I see it,” Sen. Richard Blumenthal (D., Conn.) said of potential Republican votes for calling witnesses. “All of the hand-wringing and furrowed brows seem to mean nothing.”

Sen. Bob Casey, Toomey’s Democratic colleague from Pennsylvania, said: “I don’t understand why they’re so afraid of putting people under oath."

Democrats argue that the only way to have a fair trial and verdict is for lawmakers to gather all the information they can before ruling, and that history will judge those who refuse. Republicans say Democrats haven’t directly connected their evidence to the president, even as Trump blocks people with personal knowledge of his actions from speaking.

Casey and every Senate Democrat voted in favor of motions Tuesday to call witnesses and subpoena additional documents, but Republicans blocked that move in strictly party-line votes.

GOP senators, even those who have expressed openness to witnesses, argue that they should follow the same procedure used in the 1999 impeachment trial of President Bill Clinton, when witnesses were called only after opening statements by each side. Further votes are expected later in the trial.

White House attorneys have blasted Democrats for arguing that their case is “overwhelming” — but that they also need more witnesses. If Democrats wanted more evidence they should have conducted a longer, more thorough investigation before impeaching him in the House, Trump’s attorneys argued.

“The Senate agreeing to pick up and carry on the House’s inadequate investigation would set a new precedent that could incentivize frequent and hasty impeachments,” said Senate Majority Leader Mitch McConnell (R., Ky.). “The Senate is not about to rush into these weighty questions without discussion and deliberation.”

Democrats say the Clinton trial is a poor comparison, since every critical witness in that case had testified before the trial began. In this instance, Trump has blocked critical witnesses, refused to release documents, and bragged about it during an appearance Wednesday at the World Economic Forum. “Honestly, we have all the material. They don’t have the material,” Trump said in Davos, Switzerland.

Bolton only announced his willingness to testify after the House investigation concluded. If he spoke, he would become the person closest to Trump to publicly reveal his knowledge of the president’s actions toward Ukraine.

Any push for his testimony, though, could run into a GOP effort to subpoena the Bidens, who are at the center of an unfounded theory, pushed by Trump, that the former vice president used his influence to aid a Ukrainian gas company that employed his son. There is ample evidence debunking that claim.