(CNN) New evidence showing Donald Trump's direct role in pressuring Ukraine for political favors is dialing up the heat as Republicans launch their New Year push to shield the President in a swift Senate impeachment trial.

Trump's top Senate protector, Majority Leader Mitch McConnell, is expected to attempt to define the next phase of the drama on Friday morning with his first floor speech of 2020. It was not clear whether the aftermath of the stunning US strike to kill Qasem Soleimani, Iran's top military and intelligence officer in Iraq, would change plans on Capitol Hill. The attack has the potential to scramble political calculations in Washington, in addition to its huge global implications.

Whenever McConnell plays his next card, he is expected to push back on demands by Democrats to call senior current and former White House officials to testify in the trial after the President refused to allow them talk to House investigators.

McConnell's speech will ratchet up pressure on House Speaker Nancy Pelosi, who presided over Trump's historic shaming last month but tried to bolster Democratic demands for new witnesses by declining to transmit articles of impeachment to the Senate. That means the trial -- once expected to start as soon as next week cannot yet start.

And calls for the Senate to broaden the investigation are resonating amid recent revelations that appear to bolster the impeachment case that Trump froze military assistance from Ukraine partly to coerce it to dig for dirt on his possible 2020 election rival Joe Biden.

Documents reviewed by the "Just Security" website show that a top White House budget official made clear the order to halt nearly $400 million in aid came directly from the President.

The story suggests that there could be new and damning bombshells in piles of official evidence that the President has refused to hand over to the House investigation. It offers a rationale why the White House might be keen to get the Senate trial over quickly before even more damaging evidence emerges.

"As part of our impeachment inquiry, the House subpoenaed these very documents," House Intelligence Committee Chairman Adam Schiff said in a statement on Thursday. "From their deeply incriminating character, we can now see why they were concealed: They directly corroborate witnesses who testified that military aid to Ukraine was withheld at the direction of the President and that the White House was informed doing so may violate the law."

But Republicans claim that it is not the Senate's job to improve the impeachment case sent over from the House -- and point to the failure of Pelosi to launch court challenges to compel senior White House officials who Democrats now want called to the Senate to testify in the House probe.

Critical Capitol Hill battles

While the Senate trial is almost certain to acquit Trump of high crimes and misdemeanors, the Capitol Hill exchanges in the next few days represent a vital twist in the story.

Both sides are playing a game within a game -- seeking to mold a public narrative about the trial which could have vital political consequences only 11 months from Election Day.

Democrats are seeking to convince Americans that the GOP is cooking the trial to shield an unchained President guilty of committing a dangerous abuse of power -- soliciting foreign interference in a US election.

Republicans, welded inexorably to their norm-busting President owing to his stranglehold on GOP voters, are framing Pelosi's refusal to hand over articles of impeachment as proof Democrats have a weak case no matter how convincing the evidence delivered in testimony by career foreign policy officials.

The showdown reflects how the adversarial grouping of lawmakers and voters into two rival teams threatens Congress' capacity to wield its own constitutional powers in a dispassionate examination of Trump's conduct and whether it is worthy of removal.

The President, who denies all wrongdoing, insisted during his New Year retreat at his Florida resort that he doesn't "really care" if he has a Senate trial or not. But his frenzied two weeks of furious tweets and searing attacks on Democrats tell a story of an agitated commander-in-chief pining for an acquittal that he can portray as vindication and use to vault into election year.

"The Witch Hunt is sputtering badly, but still going on (Ukraine Hoax!," Trump tweeted on Thursday.

"If this.... had happened to a Presidential candidate, or President, who was a Democrat, everybody involved would long ago be in jail for treason (and more), and it would be considered the CRIME OF THE CENTURY, far bigger and more sinister than Watergate!"

Pelosi's dilemma

JUST WATCHED Trump attacks Pelosi, Dems after calling for unity Replay More Videos ... MUST WATCH Trump attacks Pelosi, Dems after calling for unity 02:57

Pelosi's withholding of the articles of impeachment was meant to increase the leverage of the top Senate Democrat Chuck Schumer as he wrestles with McConnell over the shape of the impeachment trial.

The speaker did succeed in concentrating attention over the holiday break on the GOP's open efforts to protect Trump from charges he abused power and obstructed Congress' investigation.

Several top Republican senators, including McConnell, have warned that they will not play the role of impartial jurors during the Senate trial, drawing outrage from Democrats.

Their comments also discomforted several moderate Republican senators. Alaska Sen. Lisa Murkowski said she was disturbed by the majority leader's pledge to work with the White House counsel to coordinate arrangements for the trial.

On Monday, Maine Sen. Susan Collins, who faces a difficult reelection race, said on public radio in her state that it was "inappropriate" for senators to make up their mind before they had heard the evidence.

Collins also however backed McConnell's position that any decision on witnesses to be called should take place during the trial -- and not beforehand, as Schumer is demanding.

McConnell can only lose four GOP senators if plans for a trial come down to a series of majority votes in the chamber -- a dynamic that may have been on Pelosi's mind as she calculated her options late last year.

But while she can claim minor tactical victory in highlighting criticism of McConnell, the House has little capacity to force the Senate's hand. With McConnell apparently content to sit and wait for the articles -- and go on with confirming a relentless stream of conservative judges -- it's hard to see how Pelosi can engineer a strategic advantage.

Long game

JUST WATCHED Schumer on impeachment in 1999: Senate not like a jury Replay More Videos ... MUST WATCH Schumer on impeachment in 1999: Senate not like a jury 01:59

Any plan designed to wait out McConnell, the self-confessed devotee of the long game, is unlikely to work. After all, he blocked President Barack Obama's Supreme Court pick Merrick Garland for 10 months, opening the way for Trump to construct a conservative majority on the nation's top bench.

Schumer is expected to follow McConnell with his own statement on Friday after spending the holidays holding a string of news conferences trying to pile up public pressure on his rival.

"Will the Senate hold a fair trial, or will it enable a cover-up?" Schumer said on Monday. "What are Sen. McConnell and President Trump afraid of if all the facts come out?"

Uncertainty about the opening of the Senate trial is an irritant for Democratic senators running for president, including New Jersey's Cory Booker, Vermont's Bernie Sanders, Massachusetts' Elizabeth Warren and Minnesota's Amy Klobuchar who must sit as jurors -- even as they battle it out in Iowa ahead of the first-in-the-nation causes next month.

Missouri Republican Sen. Roy Blunt, a member of his party's leadership team in the chamber, predicted that the process would largely be completed in the next month, despite current wrangling.

"I think what's going to happen is pretty predictable," Blunt said on his home state's KSSZ radio station Tuesday. "The President's been invited by the speaker to come and give the State of the Union speech on February 4th. My guess is we'll be done with this by the time the President comes."