The White House has unveiled its legal defence as the Senate prepares for the start of Donald Trump’s impeachment trial on Tuesday.
The US president’s team argue that the Democrats have wrongly identified abuse of power as an impeachable offence, and that the impeachment process itself has been “irredeemably flawed”.
They will also say there is no evidence to support the claims that the president threatened to withhold aid from Ukraine until it announced an investigation into Joe Biden’s son.
Mr Trump’s team say Democrats “do not have a single witness who claims, based on direct knowledge, that the resident ever actually imposed such a condition”.
Sky’s US correspondent Cordelia Lynch has been speaking to one of the president’s lawyers to find out why they are confident he doesn’t have a case to answer.
Alan Dershowitz is no stranger to high profile and controversial clients.
He advised the defence team in American football star OJ Simpson’s murder trial and represented convicted paedophile Jeffrey Epstein – a man he told me he now regrets ever having met.
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The Harvard law professor is currently gearing up for another big case – as a member of Donald Trump’s legal team at the president’s Senate impeachment trial.
Professor Dershowitz says he’s putting aside his personal politics, but he and his wife needed some persuading from the president himself.
“My wife had great reluctance and in the end President Trump spoke to my wife and my wife made the argument why I shouldn’t do it,” he said.
“We’ve had to think this through very hard as a family. I’m a liberal Democrat. I voted against President Trump.”
His argument, he says, is based solely on the constitution.
He believes neither abuse of power nor obstruction of congress represent impeachable offences because there was no crime committed and only a court, not congress, should have the right to decide whether a president should release documents and make witnesses available.
“The two articles of impeachment don’t satisfy the constitutional criteria,” he says.
“The constitutional criteria are treason – nobody has alleged that he’s committed treason; bribery – although there has been discussion of bribery, he wasn’t charged with that; or other ‘high crimes and misdemeanours’.
“I interpret other high crimes and misdemeanours to require criminal conduct.”
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He isn’t talking taking a stance on whether or not Mr Trump has acted improperly. He acknowledges there are many things people believe he has done wrong.
The defence lawyer concedes that, in theory, a president asking a foreign power to investigate a rival is wrong.
His argument is much narrower than that though.
It rests solely on what he believes America’s forefathers meant and intended when they wrote the constitution and “the law distinguishes between a sin and crime,” he says.
Trump on trial
What is happening in the Senate now the president has been impeached
So will he let his reality TV-loving client embrace the stage and add his two-pennies-worth? Not if he can avoid it.
“All of my clients want to testify all the time,” he explains.
“They want to tell their story. But it’s far better to let the prosecution, in this case the House, make their case and then let it be rebutted.”
He doesn’t believe Mr Trump is a weak witness, just that the president would end up filling in the gaps and good prosecutors can lay dangerous perjury traps.
He’s open to other witnesses taking the stand but if Lev Parnas, an associate of Rudy Giuliani who claims the president knew all about the Ukraine pressure campaign, gets a chance to talk, then Republicans should be able to call Hunter Biden.
Ultimately, he adds, “it’s up to the chief justice.”
At Mr Dershowitz’s home, he’s turning to English treatise for inspiration, pouring over Blackstone’s Commentaries on the Laws of England.
He dictates sections from it over the phone as he works on what he will say in front of the Senate.
He knows it needs to be clear and concise and he hopes the American public will understand his “role in all this” is conditional not partisan.
It is another test of his legal skills and another example of how he is willing to represent divisive characters.
I ask him why he’s drawn to them.
“I grew up in Brooklyn as a street kid following the Holocaust,” he responds.
“Many of my family died in the Holocaust. I want to live in a country where everybody is always defended.”
He says the last thing the president told him was “good luck,” something he insists you always need.
But barring a last-minute mutiny, Republicans have already made up their mind – it is highly likely they will acquit President Trump, and there is every chance he will politically benefit from this whole process.
The longer this impeachment process goes on, the more turned off voters appear to be.