Senate Majority Leader Mitch McConnell of Kentucky attends a news conference with members of the Senate Republican Leadership after their policy luncheon on Capitol Hill in Washington, Sept. 24, 2019. Credit: Jacquelyn Martin | AP

WASHINGTON — Mitch McConnell made it clear Monday that if the House impeaches President Donald Trump, a trial in the Senate is unavoidable.

But how the Senate majority leader proceeds from there is far less known.

Should the impeachment spotlight turn to the Senate in the coming weeks, McConnell — who faces a re-election fight next year — will confront the dual pressures of minimizing political pain for his Senate majority and ensuring legitimacy and a sense of fairness for what would be only the third impeachment trial of a president in American history.

On Monday, McConnell said he was bound by existing Senate rules governing the impeachment and conviction process, amid speculation that he could simply ignore the specter of putting Trump on trial. Senior Republican aides had worked to try to tamp down that notion over the weekend.

“I would have no choice but to take it up,” McConnell said during a CNBC interview. “How long you’re on it is a whole different matter, but I would have no choice but to take it up, based on a Senate rule on impeachment.”

The Kentucky Republican — who hasn’t hesitated in the past to revise Senate rules to benefit Republicans, specifically the president’s judicial nominees — stressed he would not change them to aid Trump. That move would require the support of 67 senators, almost certainly an insurmountable threshold.

“The Senate impeachment rules are very clear,” McConnell said. “The Senate would have to take up an impeachment resolution if it came over from the House.”

Other than those statements, McConnell has given few public clues as to how he would proceed, and several Republican and Democratic officials on Monday cautioned that it was far too premature to predict how one of the most polarized Senates in decades would approach Trump’s trial.

Furthermore, the two previous presidential impeachment trials — of Andrew Johnson in 1868 and Bill Clinton in 1999 — were led by a Republican-controlled Senate with a Democrat in the White House. This time, Senate proceedings would be steered by a majority leader of the same party as that of the president on trial.

“This is uncharted territory,” said one senior Republican official, who, like others, spoke on the condition of anonymity to sketch out hypothetical scenarios.

McConnell was a third-term senator during Clinton’s impeachment trial — when he voted to convict the Democratic president on perjury and obstruction of justice charges, although Clinton was acquitted.

Now, McConnell is abiding by a 1986 memorandum written by then-Senate Parliamentarian Robert Dove, who concluded that Senate rules call for a “rapid disposition of any impeachment trial” and also require at least two-thirds’ support to avoid taking up the question of trying someone who had been impeached. Information from that memo, sent to reporters over the weekend, was also distributed to Republican senators, according to a senior GOP aide.

“McConnell knows the rules about as well as anybody I’ve ever known,” said former Senate majority leader Trent Lott, R-Mississippi, who held McConnell’s job during the Clinton’s impeachment trial. “He also will have the best possible advice on what the Constitution requires.”

But senior party officials have also raised the prospect that Senate Republicans could simply move to dismiss any articles of impeachment — a maneuver that failed during Clinton’s impeachment trial in January 1999 but would have a far likelier chance of succeeding with GOP control of the Senate.

Back then, former senator Robert Byrd, D-West Virginia, offered the dismissal motion that would have effectively ended Clinton’s Senate trial. But Republicans who controlled the chamber, as well as then-Sen. Russell Feingold, D-Wisconsin, voted to sustain the proceedings, denying Democrats the simple majority needed to dismiss the trial on a 56-44 vote.

Should Republicans try this tactic now, at least four GOP senators would have to align with all 47 senators in the Democratic caucus to keep the impeachment trial alive. Democrats are sure to target Senate Republicans such as Susan Collins of Maine, Cory Gardner of Colorado, Mitt Romney of Utah and Ben Sasse of Nebraska — senators who are either facing competitive re-election campaigns next November or those who have publicly voiced discomfort with Trump’s behavior as he urged Ukraine to investigate former vice president Joe Biden and his family.

If he were to take this route, McConnell would most likely let the proceedings play out for some period of time to give the trial an air of legitimacy. Clinton’s impeachment trial opened Jan. 8, 1999; the vote to dismiss the charges came Jan. 27.

The majority leader alluded to the timing issue in the CNBC interview, noting that while his hand is forced on the actual trial proceedings, “how long you’re on it is a whole different matter.”

Still, Republicans caution that much remains unknown that could alter McConnell’s political calculus if the Senate faces an actual impeachment trial. There is no way of knowing, for example, what new information will be unearthed through House depositions and subpoenas.

On the other hand, Republicans also noted that should House Democrats turn the impeachment proceedings into a sharply partisan endeavor, it would be easier to shorten the process once it reached the Senate.

“We don’t know what this football looks like when it gets over to us,” said another senior Republican official, who spoke on the condition of anonymity to discuss the matter frankly.

In public, Senate Republicans have primarily taken one of two approaches on the impeachment proceedings against Trump: Say little of substance and defer to the ongoing process, or aggressively defend the president and label Democrats as an embittered party bent on ousting Trump.

Meanwhile, two Senate committee chairmen signaled an aggressive tack Monday, as they made public a letter sent to Attorney General William P. Barr last week pressing him to investigate potential coordination between Ukrainian officials and the Democratic Party during the 2016 campaign. Ukrainian officials have denied any effort to help Hillary. Clinton.

“Ukrainian efforts, abetted by a U.S. political party, to interfere in the 2016 election should not be ignored,” Senate Finance Chairman Chuck Grassley, R-Iowa, and Homeland Security and Governmental Affairs Chairman Ron Johnson, R-Wisconsin, wrote in the letter. “Such allegations of corruption deserve due scrutiny, and the American people have a right to know when foreign forces attempt to undermine our democratic processes.”