The Senate acquitted Donald Trump, only the third president to be impeached, on charges he abused his power and unjustly stonewalled Congress, clearing him to focus on a bare-knuckle re-election campaign and raising new questions about the powers of his office.

Expansive arguments from his made-for-television legal team about presidential powers and sometimes-contradictory defences of the New York real estate executive and former reality television star ultimately won the day. House Democrats' warnings that an acquittal verdict could cause Mr Trump to repeat what they described was an attempt to "shake down" another world leader in order to "steal" an American election failed to sway Republican senator-jurists.

Mr Trump's presidency, which has had a Teflon-like quality and endured one self-inflicted wound after another, will continue as he survived the most serious rebuke House Democrats could hand down. As Democrats grapple with their defeat at the hands of Republican senators who again backed a man most of them just a few years ago condemned, Mr Trump's approval rating has been climbing and they have no clear nominee with a plan to unite their party's factions and defeat him in November.

In a remarkable statement that echoed many of his Republican mates, retiring Tennessee Senator Lamar Alexander said he would effectively kill any motion to call new witnesses. But he also plainly stated his and other Republican jurists' view that the House Democratic impeachment managers had proven their case.

In short, Mr Alexander told the world he – and other GOP senator-jurists – believe Mr Trump tried to carry out what House Intelligence Committee Chairman Adam Schiff called a "shakedown" of Ukraine's new and inexperienced president.

Donald Trump celebrity president: A decade in two halves Show all 29 1 /29 Donald Trump celebrity president: A decade in two halves Donald Trump celebrity president: A decade in two halves Trump styles his 'You're fired!' pose in his Trump Tower office in June 2012. At the time he was known as a reality TV star on The Apprentice Diane Bondareff/Invision/AP Donald Trump celebrity president: A decade in two halves He was also well known as the patron of the Miss Universe competition Getty Donald Trump celebrity president: A decade in two halves Early signs of Trump's ambition for the presidency can be found everywhere. Not least in his 2011 book 'Time to get tough: Making America #1 again' Getty Donald Trump celebrity president: A decade in two halves Trump with Piers Morgan in November 2010. Piers Morgan has long held that he and Trump are good friends Getty Donald Trump celebrity president: A decade in two halves Trump appeared on Fox & Friends, his favourite show, in August 2011 Getty Donald Trump celebrity president: A decade in two halves Trump considered running in the 2012 election, where he would have faced Barack Obama. He is speaking here at an event for a Republican women's group Getty Donald Trump celebrity president: A decade in two halves Trump was subject to a Comedy Central roast in 2011. He is pictured here being roasted by rapper Snoop Dogg Getty Donald Trump celebrity president: A decade in two halves Given that this Trump store is in the lobby of Trump Tower, it can be said that Trump sells merchandise of himself out of his own home Getty Donald Trump celebrity president: A decade in two halves Trump held meetings with prominent Republicans when considering his 2012 bid. 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. Ultimately he was declared the Republican candidate in June 2016 Getty Donald Trump celebrity president: A decade in two halves Trump took part in the TV debate against opponent Hillary Clinton on 9 October Getty Donald Trump celebrity president: A decade in two halves Trump and wife Melania vote in the presidential election on 8 November 2016 AFP/Getty Donald Trump celebrity president: A decade in two halves Hillary Clinton conceded defeat at 2:50am on 9 November and president-elect Trump swiftly delivered his victory speech to a crowd of supporters Getty Donald Trump celebrity president: A decade in two halves News coverage around the world focused on the huge political upset that Trump's victory spelled AFP/Getty Donald Trump celebrity president: A decade in two halves Trump met with president Obama to discusss transition planning on 10 November. 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. He is standing here in front of a prototype for a section of the wall Getty Donald Trump celebrity president: A decade in two halves Trump's meetings with other world leaders have provided no short supply of photo opportunities Getty Donald Trump celebrity president: A decade in two halves Trump was welcomed to the UK by the Queen and a state banquet was held at Buckingham Palace in his honour Reuters Donald Trump celebrity president: A decade in two halves Not everyone welcomed the president. Mass protests were held in London throughout his visits in both 2018 and 2019 EPA Donald Trump celebrity president: A decade in two halves One of the most significant meetings Trump has held with another leader was with North Korea's Kim Jong Un. In June 2019, Trump became the first sitting president to set foot in North Korea Getty Donald Trump celebrity president: A decade in two halves 2020 will see president Trump fight for a second term in office, who knows what the next decade will bring? Getty

"There is no need for more evidence to prove something that has already been proven and that does not meet the United States Constitution's high bar for an impeachable offence," he said. "There is no need for more evidence to prove that the president asked Ukraine to investigate Joe Biden and his son, Hunter; he said this on television on October 3, 2019, and during his July 25, 2019, telephone call with the president of Ukraine."

Lawmakers and legal scholars already are debating the long-term implications of Mr Trump's acquittal. That's largely because of arguments made by Alan Dershowitz, a celebrity law professor the president recruited after relishing his anti-impeachment cable news appearances.

"If the president does something that he thinks will help him get elected, in the public interest, that cannot be the kind of quid pro quo that results in impeachment," Mr Dershowitz, Harvard University professor, told senators. He was responding to a question from GOP Texas Senator Ted Cruz about whether a president ordering a quid pro quo would ever be legally appropriate. The question's premise also touched on the legality if such an order by a sitting president was made with Election Day in mind.

"Every public official I know believes that his election is in the public interest," Mr Dershowitz replied. "Mostly, you're right."

That raised alarms among Democrats and some legal scholars, who warn the acquittal verdict will make Dershowitz's view of presidential powers part of American legal canon. So, too, did the defence team's contention – again, via Dershowitz – that Mr Trump might have acted unjustly, but because he is the president, those actions fail to meet the high standards of impeachment and removal.

That could mean that if another candidate in Mr Trump's harsh populist mold wins the presidency down the line, "many of the rails are now off – he system is now much easier to exploit," said Marc Hetherington, a political science professor at the University of North Carolina.

Trump attorney Alan Dershowitz uses Middle East Peace Plan to explain quid pro quos during impeachment hearing

"It is a reminder that in a democracy that runs more on norms than rules, the character of the people occupying the institutions is centrally important," Mr Hetherington said.

At one point late on the defence team's first day of making its case, the Harvard law professor claimed nothing in Mr Trump's actions toward Ukraine's new president – including asking him to "do us a favour though" after they had just discussed a $391m military aid package the latter needed to guard against Russia – "would by itself constitute an abuse of power".

"A quid pro quo alone," Dershowitz added, "is not the basis for an abuse of power." Some warn Dershowitz, validated by GOP senators, has made it legally and politically acceptable for Mr Trump and future presidents to use taxpayer-funded military equipment to get foreign leaders to carry out what House Democrats called the "dirty work" of finding dirt on their US political rivals.

"We saw the president continue to move the goalposts. You know, at first, they're saying, 'There is no quid pro quo.' Then they're saying that the quid pro quo is unimpeachable," said Congressman Jason Crow, one of the House Democrats' impeachment managers.

"Then when it becomes clear to everyone in that room and the American people that what the president did was wrong and he did it, they're just saying, 'Move on because what the president does is just presumptively the right thing," Crow added.

Senate Minority Leader Chuck Schumer said if the defence team's arguments become accepted legally, it also could stop lawmakers not of a president's party from investigating him or her – and "spell the end of presidential accountability as we know it".

William Galston, who worked in the Bill Clinton White House, said the verdict might lead "many Americans to conclude that Trump's theory of the unfettered presidency is basically correct," adding: "This would represent a dangerous turning point for our constitutional system."

But Patrick Philbin, deputy White House counsel, pushed back, saying their case merely was about defending their client against a flawed case on which House Democrats' prosecution was built.

Ted Cruz and other Republican senators took a much different view of Dershowitz's legal theories. The Texas lawmaker, a fierce Trump critic-turned-loyalist, told reporters the Harvard professor laid out a "powerful argument".

"Professor Dershowitz rightly pointed out that we engage in quid pro quo's all the time," Mr Cruz said of US foreign policy. "That's not the question. The question is whether the president committed a high crime or misdemeanour and if he's asking for investigations into possible corruption when there is real and credible evidence that there might be corruption, that is not an impeachable offence.

Alan Dershowitz says abuse of power is not impeachable

Mr Trump's views on presidential powers were given a boost when GOP senators opted against hearing from witnesses that might have given them pause about how the Oval Office incumbent uses those authorities.

"If this trial wraps up in the next 24 to 48 hours without witnesses, he can say, 'I was acquitted,' but he can't say, 'I was exonerated," Senator Angus King, a Maine independent who caucuses with Democrats, said. "We're having no witnesses in the Senate, ad that's never happened before. ... I opposed impeachment for the last two-and-a-half years ... The problem with the Ukraine business ism it appears anyway, that it was the president's effort to affect the upcoming election.

"The question is: Is the election a check if the election itself is in play from the point of view of the president's own actions?" King asked rhetorically.

That answer is just over nine months away. That's when voters will head to the polls and decide whether Mr Trump deserves a second term after being impeached and overseeing the most chaotic and unpredictable presidential terms in American history.

As Democrats reel from their latest defeat to a man who largely has bested them since 2016, Mr Trump already has pivoted into re-election mode – complete with more of his signature bold campaign-trail promises.