WASHINGTON (Reuters) - U.S. President Donald Trump’s impeachment trial, which begins next week, may pose one of the greatest political challenges Senate Majority Leader Mitch McConnell has faced in more than three decades in Congress. As usual, he is showing little sign of the pressure.

FILE PHOTO: U.S. Senate Majority Leader Mitch McConnell (R-KY) faces reporters with fellow Senate Republicans following their weekly policy lunch on Capitol Hill in Washington, U.S., January 7, 2020. REUTERS/Leah Millis/File Photo

McConnell, the top Republican in Congress, says America’s founders created the Senate for moments such as this, to block the “factional fevers” and “runaway passions” of the House of Representatives.

The reserved Senate leader, who represents Trump-friendly Kentucky, views with contempt the allegations by the Democratic-controlled House that the Republican president abused his power.

McConnell says there is no chance Trump will be convicted on charges that also include obstructing a congressional investigation into his conduct. The House formally impeached Trump on Dec. 18 and last week sent the two accusations to the Senate for trial.

Just hours before the 100 senators were to be sworn in as jurors in that trial, McConnell said the Senate would tame the House’s unruly Democrats and “put aside animal reflexes and animosity” in order to “cooly consider” the charges.

McConnell is walking a dangerous high wire: He has openly demonstrated he will work to protect Trump, which could help his own re-election in November. But political crosswinds push him to simultaneously give moderate Republican senators -- some also up for re-election this year -- the leeway to at least consider having witness testimony that could damage Trump.

How McConnell handles this challenge could help determine whether Republicans maintain their Senate majority - and he keeps his position as majority leader - in November. In any case, all sides are likely to assign him much of the credit or blame for how the trial proceeds.

That is unlikely to faze him, colleagues say.

“I don’t know any human being, anywhere, that deals with pressure better than Mitch McConnell,” said Senator Kevin Cramer, a Republican.

A shrewd negotiator who plays hardball politics at a level unusual even by Washington standards, McConnell is a self-proclaimed “Grim Reaper” who prides himself on blocking Democratic initiatives.

When McConnell takes a stand, he is difficult to budge, said Dick Durbin, the Senate’s number-two Democrat.

“He only moves if he’s personally concerned about his own re-election or the election of his majority,” Durbin told reporters last month, noting, “2020’s an election year.”

First elected in 1984, McConnell easily won his last campaign in 2014 but could face a stiff challenge this year.

As one-half of a Washington power couple (McConnell’s wife, Elaine Chao, serves as Trump’s secretary of transportation), the senator says he is working in “total coordination” with the White House in preparing for the trial.

The Trump-McConnell relationship was not always a smooth one.

In 2017, after the Senate failed to repeal major elements of the Affordable Care Act, also known as Obamacare, Trump tweeted, “Can you believe that Mitch McConnell, who has screamed Repeal & Replace for 7 years, couldn’t get it done.”

Now, Trump, 73, and McConnell, 77, say they speak regularly.

On the surface, the six-term senator and Trump could not be more different.

Trump, a former reality television star and businessman, rarely misses opportunities to boast about himself and attack opponents.

The laconic McConnell eschews social media, can be hard-pressed to make small talk, sometimes sits silent in meetings, according to those who have attended, and can repel reporters’ questions by refusing to utter a syllable.

“As he sometimes says, he likes to allow himself the luxury of the unexpressed thought,” said Rohit Kumar, who worked for McConnell from 2007-2013 and was a deputy chief of staff.

Trump and McConnell do share some traits. Both have seized key moments to flex their muscles in ways that opponents say unduly stretches the bounds of their powers.

Trump, for example, funded construction of some parts of the U.S.-Mexico border wall by taking money dedicated to other programs, an unusual step taken in defiance of Congress.

In 2016, McConnell enraged Democrats by refusing to consider then-President Barack Obama’s choice of federal Judge Merrick Garland to serve on the Supreme Court after the death of conservative Justice Antonin Scalia. Had Garland been confirmed by the Republican-controlled Senate, he would have tipped the court in a liberal direction.

For all his doggedness, Democrats think McConnell can at times be pressured into bending. Speaking on the Senate floor last year after being dubbed “Moscow Mitch” by some critics for his refusal to allow additional election security funding, McConnell said: “This modern-day McCarthyism is toxic.” Shortly afterward, the extra funds flowed through the Senate.

Kumar said McConnell’s taciturn style, punctuated by silences, can force those sitting across the negotiating table to fill the uncomfortable void by tipping their hands.

People are “endlessly vexed by McConnell’s patrician, silent nature. He doesn’t need to fill the silence with his own voice,” Kumar said.

McConnell has had frosty relations with Senate Democratic Leader Chuck Schumer and his predecessor, Harry Reid.

One former senior Senate Democratic aide said that when Reid and McConnell were thrown together, conversation about baseball was the only safe territory for two men who never established a good working relationship.

McConnell and Schumer served in the Senate during Bill Clinton’s 1999 impeachment trial - McConnell voted to convict the Democratic president; Schumer voted to acquit.

So far, these two experienced hands, operating in arguably the most partisan atmosphere in U.S. political history, have not found a way to tame the “factional fevers” raging over Trump’s impeachment.