Michael Cohen could make or break Trump hush-money trial

The prosecution's star witness in Donald Trump's Manhattan criminal trial may also be its biggest liability.

Michael Cohen, Mr Trump's former personal lawyer, took the stand in the ex-presidents trail and testified against the man he once reverently referred to as "The Boss."

Cohen made the hush-money payment at the centre of the case, a sum the prosecution alleges was fraudulently reimbursed by Mr Trump. His claims, which he made during four days of testimony, are at the centre of prosecutors' case.

Not only did he allege that Mr Trump fraudulently repaid him for the hush-money sum, but he claimed that he kept his former boss updated on every step of the effort to conceal the alleged tryst with an adult-film star.

But outside the courtroom, on podcasts, television and social media, Cohen has not exactly helped their case - something Mr Trump's legal team made note of in court.

Cohen has mocked Mr Trump on X, calling him "sleepy Donald" and has used a profane nickname to refer to the former president and his lawyers. Cohen also has posted memes that appear to show Mr Trump in prison-uniform orange - which were shown in court - and joked on TikTok about Mr Trump being incarcerated.

"Trump 2024?" he said during one TikTok stream, reported by ABC News. "More like Trump 20-24 years."

Cohen's actions went too far for Justice Juan Merchan, who had to warn prosecutors to tell Cohen to stop commenting on the case.

One of his lawyers, Jeffrey K Levine, told the BBC, "I have no doubt that Michael will cooperate with whatever the court's asking him to do. Or not to do."

The district attorney's office did not return a request for comment about their star witness.

Cohen eventually announced that he would not make any further comments on his social media regarding the case, writing: "Despite not being the gagged defendant, out of respect for Judge Merchan and the prosecutors, I will cease posting anything about Donald on my X (formerly Twitter) account or on the Mea Culpa Podcast until after my trial testimony. See you all in a month (or more)."

Still, his rogue behaviour - coupled with his very real criminal record - opened the door for Mr Trump's defence to cast doubt on this crucial player.

During cross-examination, defence lawyer Todd Blanche pilloried Cohen for his insults and negative comments about the former president. He used the statements to discredit Cohen, and attempted to paint him as a vengeful man committed to punishing a boss who spurned him.

"He's a real headache," said Lance Fletcher, a former Manhattan prosecutor who now practises criminal defence. "He's doing everything as a prosecutor you don't want your witness to do. He's got all sorts of credibility problems."

In 2018, Cohen pleaded guilty to eight felony counts including tax offences, fraud and campaign finance violations. The latter charge stemmed from the very same hush-money payment at the heart of Mr Trump's case.

He also pleaded guilty to lying to Congress - a fact Mr Trump's attorneys brought up in this trial and during a separate civil case.

Mr Trump is charged with 34 counts of falsifying business records for allegedly reimbursing Cohen for a $130,000 hush money payment he made to adult-film star Stormy Daniels, then trying to disguise records of the payment as legal expenses.

Ms. Daniels has alleged that she had sex with Donald Trump in 2006. Mr Trump has pleaded not guilty to the charges and denied any sexual encounter with Ms Daniels.

Mr Blanche, Mr Trump's lead attorney, worked to undercut Cohen as a witness in his opening statement. He said Cohen remained "obsessed" with Trump "to this day," and that he "rants and raves" about the former president.

BBC News reporters are in the Manhattan courtroom covering the historic first criminal trial of a former US president. You'll find their updates and analysis on the BBC news website and app, and across TV, radio and podcasts.

"I submit to you that he cannot be trusted," Mr Blanche said.

Mr Fletcher agrees with the defence's strategy. "You almost want to make the case about him," he said.

The defence did that so effectively that prosecutors asked Cohen at one point whether he was the one on trial, just to clarify for the jury.

But the prosecution mainly used Cohen to link the alleged cover-up of the hush money payment directly to the former president. Prosecutors asked whether he discussed the matter with Mr Trump and took direction from him, and the ex-lawyer alleged that he had.

Mr Blanche and his colleagues did bring up Cohen's previous comments while he's on the stand, and called into question his motivation for providing damaging testimony against Mr Trump. His attorneys already alleged before the trial that Cohen is profiting off Mr Trump's legal problems through his podcast, TikTok streams, and books - a point they stressed while questioning the ex-fixer.

Mr Fletcher said that the defence would likely press on this and how it affected his family to rile Cohen up, but he came across as unflappable during his testimony. There were only a few times when he appeared bothered by the questioning.

Cohen has not always stayed calm while on the stand.

When he testified at Mr Trump's civil business fraud trial last year, he got into a brief shouting match with one of the former president's lawyers after she repeatedly called his credibility into doubt.

During her time as a prosecutor, former New York State Acting Supreme Court Justice Diane Kiesel used to have a saying: "I don't go to central casting for my witnesses."

In other words, prosecutors do not always get the perfect witness to prove their case - some may provide essential testimony, but are flawed. Manhattan District Attorney Alvin Bragg is in a similar position with Cohen, she said.

"Who do you think is going to be making hush-money payments to a porn star?" former Judge Kiesel said. "Some upstanding member of the bar... who everyone looks up to as a paragon of legal ethics?"

She said that Mr Bragg's team must "go through every single thing that Michael Cohen has to say" on the stand and offer corroborating evidence to convince the jury - and that is just what they did.

Wherever they could, prosecutors attempted to provide other witnesses or evidence that could corroborate Cohen's claims.

Prosecutors have introduced a paper trail of texts, emails, phone calls, bank records and legal contacts Cohen left as he brokered payouts to Ms Daniels and another woman, Playboy model Karen McDougal, in exchange for their silence.

They also called on people like former tabloid publisher David Pecker and Ms Daniel's former attorney Keith Davidson, to shed light on events involving Cohen and the hush-money payments that he made.

They are hoping these may buoy Cohen, who has been caught lying under oath, and keep jurors from entirely dismissing his testimony. That is something that the jury could do if they decide he is not credible.

Prosecutors did not shy away from acknowledging Cohen's flaws in the courtroom.

During opening statements, assistant district attorney Michael Colangelo told the jury: "You will need to keep an open mind" about Cohen, and "keep in mind all the evidence that corroborates Michael Cohen's testimony".