After all that, it all could be over sometime on Friday.

Donald Trump appears to be on a metaphorical bullet train to acquittal on charges of abusing the power of the presidency and unjustly stonewalling Congress. And one of his once most unlikely of allies, Senate Majority Leader Mitch McConnell, is the conductor.

The president appeared on Wednesday evening to sense the Senate could move by week's end to a final vote on the House's two articles of impeachment, tweeting simply: "GAME OVER!" Mr Trump's words were displayed over a video clip from last summer of John Bolton, his former national security adviser, echoing his then-boss about fighting corruption in Ukraine being in America's national interests.

Democrats want Mr Bolton to testify in the trial after details of his coming book leaked on Sunday, including a portion in which the former White House official wrote he heard Mr Trump directly link a massive military aid package to the new Ukraine government to it announcing investigations of top US Democrats, including former Vice President Joe Biden, a leading 2020 presidential candidate.

But there were growing signs on Wednesday evening that Mr McConnell, considered a masterful behind-the-scenes tactician, had swayed several wobbly members of his caucus to oppose joining Democrats in voting to subpoena Mr Bolton's testimony.

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He is pictured here with Alaska governor Sarah Palin Getty Donald Trump celebrity president: A decade in two halves He didn't end up running in 2012 afterall, instead endorsing Republican candidate Mitt Romney AFP/Getty Donald Trump celebrity president: A decade in two halves Trump's golf course in Aberdeen proved controversial in 2012 when he began lobbying the Scottish government against wind power in order that they wouldn't install turbines off the shore by his new course Getty Donald Trump celebrity president: A decade in two halves He even gave evidence to a Scottish parliamentary committee discouraging wind energy AFP/Getty Donald Trump celebrity president: A decade in two halves He still found time for a round of course AFP/Getty Donald Trump celebrity president: A decade in two halves On 16 June 2015, Trump announced that he would run for the presidency of the United States in the 2016 election as a Republican Getty Donald Trump celebrity president: A decade in two halves His campaign was divisive, courting controversy wherever he went. 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AFP/Getty Donald Trump celebrity president: A decade in two halves Donald Trump and Nigel Farage pose in the golden elevator at Trump Tower on 12 November 2016. Farage was the first British politician to meet with Trump after the election LeaveEUOffical/Twitter Donald Trump celebrity president: A decade in two halves The inauguration of Donald Trump took place on 20 January 2017. Trump's press secretary Sean Spicer boasted that the crowd was the 'largest ever' to witness an inauguration, a claim that was proved not to be true Getty Donald Trump celebrity president: A decade in two halves In his first 100 days as leader, Trump signed 24 executve orders, the most of any president AFP/Getty Donald Trump celebrity president: A decade in two halves One of Trump's most memorable election pledges was to build a wall between the US and Mexico. 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Getty

"I'm ready to vote on final judgement," Senator John Barrasso told reporters. The Wyoming Republican is a member of Mr McConnell's leadership team (read: his inner circle), and has become a barometer of what the top Senate Republican is thinking.

"Yes, that's the plan," Mr Barrasso replied when asked if Republican leaders intend to skip any votes on witnesses and go instead on Friday to final votes on the two House-passed articles of impeachment.

Notably, a source familiar with Mr McConnell's thinking did not deny that is the leader's intention when pressed by The Independent.

Senate Democrats used part of their questions for Mr Trump's legal team and House Democratic impeachment managers on Wednesday to make the case that a trial without witnesses is anything but. (The Trump defence team, however, argued that in the previous two presidential impeachment trials, the Senate heard only from witnesses the House had interviewed.)

Despite the seemingly orchestrated questions and answers between House Democratic impeachment managers and Senate Democrats, their leaders by day's end appeared to signal defeat is near.

"We've always known it will be an uphill fight on witnesses and documents because the president and Mitch McConnell put huge pressure on these folks," Senate Minority Leader Chuck Schumer said on Wednesday, during a break in the questioning.

"Is it more likely than not?" the New York Democrat said of Bolton and other witnesses being called. "Probably no."

Schumer: 'Trump tried to blackmail Ukraine'

Senator Ted Cruz earlier this week summarised the thinking of many Republican lawmaker-jurists, calling votes on witnesses and acquittal collectively an "easy and straightforward vote".

"I don't think any additional witness testimony is necessary," the Texas Republican said, saying he does not believe House Democratic managers have "come close to proving their case". He added that many Republican senators believe the House prosecutors failed to prove their own case that Mr Trump's insistence on securing from Ukraine investigations of the Bidens was "phony" and "baseless" and a "scam" to help him win re-election.

By Thursday morning, Democrats were acknowledging that Mr Trump by Friday likely will become the third sitting American president ever to be impeached and then cleared by the upper chamber.

"We know he's not going to be removed from office. There aren't 67 votes ... to remove him," David Axelrod, a former senior adviser to former President Barack Obama told CNN. "It's not going to happen."

That means the president's legal team's contention that a sitting chief executive's actions - unless clearly criminal - always are in the country's interests soon could become precedent.

Representative Jason Crow, a House impeachment manager, said on Thursday that means the legal team will have successfully argued "that the president is above the law".