Senate Majority Leader Mitch McConnell of Ky., speaks on the Senate floor, Friday, Jan. 3, 2020 at the Capitol in Washington. Credit: Senate TV | AP

The U.S. House of Representatives has voted to impeach President Donald Trump, and now it’s the U.S. Senate’s constitutional role to conduct an impeachment trial and determine whether or not to convict him and remove him from office.

Much has been made, and for good reason, about the oath senators will take as part of the trial, affirming their commitment to doing “impartial justice” in the process. Both Sens. Susan Collins and Angus King have made reference to that oath in recent weeks.

“It is inappropriate, in my judgment, for senators on either side of the aisle to prejudge the evidence before they have heard what is presented to us, because each of us will take an oath, an oath that I take very seriously to render impartial justice,” Collins told Maine Public this week when asked about Senate Majority Leader Mitch McConnell’s discouraging comments in December that he would work in “total coordination” with the White House on impeachment.

She also said there are Democratic members of the Senate who are “not giving the appearance of and the reality of judging this in an impartial way.”

Collins has familiarly emerged an outlier in the Senate Republican caucus by offering any sort of rebuke to McConnell — and that’s not insignificant at this stage.

Following the House impeachment vote, King referenced the Senate’s impeachment oath, and said he “will do everything I can to fulfill this new oath as well as my core oath to uphold and defend the Constitution.” And after McConnell’s coordination comments, King said on Twitter that “History will record that this is not only a trial in the Senate — it is a trial of the Senate.”

Perhaps the Senate’s biggest test will be how it deals with the question of whether or not to seek additional witness testimony and evidence not included in the House investigation.

“I am open to witnesses,” Collins told Maine Public on Tuesday. “I think it’s premature to decide who should be called until we see the evidence that is presented and get the answers to the questions that we senators can submit through the chief justice to both sides.”

Sen. Chuck Schumer, the Democratic leader in the Senate, has called for an agreement about additional witnesses and documents before the trial process moved forward. McConnell, on the other hand, has suggested that the process for then-President Bill Clinton’s impeachment trial serve as a template. Under that scenario, the Republican Senate majority would have a chance to dismiss the articles of impeachment against President Trump, after hearing from the House managers arguing for impeachment and from the White House’s response, but before a vote on any other potential witnesses or evidence.

There are multiple additional witnesses we’d like to see testify under oath in the Senate. We would be all for some type of agreement ahead of time to secure testimony, both from potential witnesses that Democrats want such as administration officials such as former national security adviser John Bolton and acting Chief of Staff Mick Mulvaney, and from witnesses that House Republicans tried to call such as the anonymous whistleblower (who should remain anonymous in the trial) and Hunter Biden, the son of former Vice President Joe Biden, who is at the center of debate over a summer phone call between Trump and Ukraine President Volodymyr Zelensky.

Based on what we know now, and what we anticipate in those early stages, we expect the existing gaps and unanswered questions in this impeachment conversation will remain without additional testimony. And we hope individual senators will agree that these gaps need to be filled to give Americans a chance for a more complete understanding of Trump’s actions.

The BDN Editorial Board

The Bangor Daily News editorial board members are Publisher Richard J. Warren, Editorial Page Editor Susan Young, Assistant Editorial Page Editor Matt Junker and BDN President Todd Benoit. Young has worked...