Senate Majority Leader Mitch McConnell, R-Kentucky, joined by Sen. Roy Blunt, R-Missouri, left, and Sen. Joni Ernst, R-Iowa, right, dismisses the impeachment process against President Donald Trump, saying, "I'm not an impartial juror. This is a political process," as he meets with reporters at the Capitol in Washington on Tuesday. Credit: J. Scott Applewhite | AP

WASHINGTON — As President Donald Trump prepares to stand trial in the Senate next month — proceedings that were triggered with his impeachment by the House on Wednesday — senators are hurtling toward an acquittal that is all but assured but with much uncertainty about how the chamber will arrive there.

For now, there is no clarity on how long a trial will last or even when it will begin. It is almost certain that there will not be a bipartisan agreement on witnesses. With very limited exceptions, senators are taking their cues from their party leaders, with Senate Republicans increasingly coordinating with the White House on a trial strategy that they insist will be fairer than what the House afforded Trump. Adding to the uncertainty: Speaker Nancy Pelosi, D-California, late Wednesday left open the possibility the House may not immediately send the articles of impeachment to the Senate, saying she wants to know more about how the trial will proceed.

What is certain is that the bipartisan bonhomie that at least helped launch President Bill Clinton’s Senate trial two decades ago is gone. The chamber is already locked in a bitter struggle over how the proceedings for Trump will be conducted, as the two sides trade accusations of impartiality and a rush to judgment.

Even before the two men have spoken privately, the bad blood between Senate Majority Leader Mitch McConnell, R-Kentucky, and Senate Minority Leader Chuck Schumer, D-New York, has spilled into the open, with the pair trading barbs in dueling floor speeches and media interviews rather than negotiating one on one.

Yet senators are balancing their partisan roles with a desire to protect the integrity of the Senate, particularly as a recent Washington Post-ABC News poll shows that more than 6 in 10 Americans say they’re confident the Senate will give Trump a fair trial.

Some senators concede that the task may be more difficult today than it was during the Clinton impeachment.

“It’s not just the individuals, the players, but I think the game is different today than it was back then,” said Senate Majority Whip John Thune, R-South Dakota, who will play a central role in ensuring there will be a majority of GOP senators for a swift impeachment trial.

As Thune prepares for January, he met privately Wednesday with former senator Trent Lott, R-Mississippi, who as majority leader helped steer Clinton’s trial.

“For something like this, it really needs, I think, to move forward in a way that builds upon some sort of bipartisanship and some level of cooperation that suggests, you know, that it isn’t just chaos around here,” Thune said.

But any semblance of bipartisanship on setting the parameters of Trump’s trial has largely evaporated — if it ever existed.

For days, Democrats have been infuriated at McConnell’s public acknowledgment that he was coordinating with the White House — a complaint Republicans have shrugged off, saying they don’t consider themselves impartial jurors in what they contend is a political process.

Schumer fired the opening shot in the trial negotiations this week, requesting the testimony of four witnesses from the Trump administration who had rebuffed requests and subpoenas from the House to testify in its impeachment inquiry. Schumer has threatened to force floor votes during a trial on calling those witnesses.

McConnell pointedly noted that Schumer went to the news media with his requests first rather than to him. Thune said the minority leader’s tactic “just rubbed a lot of our members the wrong way.”

Indeed, Schumer’s offer was designed largely to pressure a handful of GOP senators who Democrats think could break with their party and demand that the Senate hold a more thorough trial because they face tough re-election contests or are retiring or considering how their role in the impeachment battle will affect their legacies.

“We have to do everything we can to conduct a fair trial, but whether that happens depends on whether or not we can find four Republicans who will vote to do this the right way,” said Sen. Brian Schatz, D-Hawaii. “Republicans have to decide whether their job is to be loyal to the Constitution or to their party.”

In the absence of bipartisan talks, Senate Republicans have intensified their coordination with the administration in recent days. McConnell — who has made clear his preference for a limited trial with no witnesses — has been in regular contact with the president and his legal team, according to GOP officials who spoke on the condition of anonymity to discuss the private talks.

On Capitol Hill, Senate Republicans have regularly fielded visitors from the administration, such as White House Counsel Pat Cipollone, Vice President Mike Pence and, on Wednesday, White House counselor Kellyanne Conway, who met with GOP senators for lunch to discuss impeachment strategy.

Inside the meeting, Conway presented a ream of recent polling, making the case that public sentiment in recent weeks has turned against the Democrats’ efforts to impeach the president, according to senators who attended.

“You see increasingly, the polling is going in favor of no impeachment and removal from office,” Conway said as she left the lunch.

Public polling his consistently shown that Americans are about evenly split on whether to impeach the president.

As to the trial structure that the White House prefers, Conway told reporters: “I think short versus long is less important than full and fair.”

Senate GOP leaders hope to make a final decision on witnesses deep into Trump’s trial, after both the House impeachment managers and the president’s defense team have had ample time in the well of the chamber to make their arguments. At that point, senior Republicans hope there will be 51 senators who will be ready to move to a final vote on acquitting Trump, short-circuiting any need for witnesses.

“We’re intent on trying not to look for opportunities that needlessly divide people until they’ve heard both cases,” said Sen. Roy Blunt, R-Missouri. “I think that’s our focus, is making sure that happens first.”

The House voted to impeach Trump on charges that he tried to leverage a White House meeting as well as military aid sought by Ukraine to combat Russian military aggression, as a means of pressuring Ukrainian President Volodymyr Zelensky to announce an investigation of former vice president Joe Biden and his son Hunter Biden, as well as a probe of an unfounded theory that Kyiv conspired with Democrats to interfere in the 2016 U.S. presidential election. The House also approved an article of impeachment that accuses Trump of obstructing Congress by preventing members of his administration from cooperating with the investigations.

Calls by Trump and White House officials to have an assortment of controversial witnesses testify in the Senate — including Hunter Biden over his role on the board of a Ukrainian energy company while his father was vice president and the Obama administration’s policy leader regarding Kyiv — have largely quieted in recent days.

“We can look at these accusations outside of impeachment,” said Sen. Lindsey Graham, R-South Carolina, a close Trump ally who chairs the Senate Judiciary Committee. “So I’m going to tell the president no to his witness request, because I think what’s best for the country is to get this behind us as soon as possible.”

Senate leaders hope to resolve at least some of the other lingering questions this week.

In a lunch with Republican senators on Tuesday, McConnell said he hopes senators will know before leaving for the holidays this week when the impeachment trial will begin in January, said a senator who was in attendance. That information was confirmed by two officials familiar with the discussion.

Once the articles of impeachment have been delivered to the Senate, the chamber will have to take them up. What the Senate does then will not be finalized until McConnell and Schumer have had a chance to discuss the trial, but senators are likely to have to reach some sort of agreement to set a trial date in January.

Washington Post writer Karoun Demirjian contributed to this report.