NEW YORK (AP) — He once said he would take a bullet for Donald Trump. Now Michael Cohen is prosecutors’ biggest piece of legal ammunition in the former president’s hush money trial.

But if Trump’s fixer-turned-foe is poised to offer jurors this week an insider’s view of the dealings at the heart of prosecutors’ case, he also is as challenging a star witness as they come.

There is his tortured history with Trump, for whom he served as personal attorney and problem-zapper until his practices came under federal investigation. That led to felony convictions and prison for Cohen but no charges against Trump, by then in the White House.

Cohen, who is expected to take the stand Monday, can address the jury as someone who has reckoned frankly with his own misdeeds and paid for them with his liberty. But jurors likely also will learn that the now-disbarred lawyer has not only pleaded guilty to lying to Congress and a bank, but recently asserted, under oath, that he wasn’t truthful even in admitting to some of those falsehoods.

And there is Cohen’s new persona — and podcast, books, and social media posts — as a relentless and sometimes crude Trump critic.

As Trump’s trial opened, prosecutors took pains to portray Cohen as just one piece of their evidence against Trump, telling jurors that corroboration would come via other witnesses, documents and the ex-president’s own recorded words. But Trump and his lawyers have assailed Cohen as an admitted liar and criminal who now makes a living off tearing down his former boss.

“What the defense is going to want the jury to focus on is the fact that he’s a liar” with a blemished past and a tetchy streak, said Richard Serafini, a Florida criminal defense lawyer and former federal and Manhattan prosecutor.

“What the prosecution is going to want to focus on is ‘everything he says is corroborated — you don’t have to like him,'” Serafini added. “And No. 2, this is the guy Trump chose.”

LOYALIST TURNED FOE

Cohen’s early-2000s introduction to Trump was a classic New York real estate story: Cohen was a condo board member in a Trump building and got involved on Trump’s side of a residents versus management dispute. The mogul soon brought Cohen into his company.

Cohen, who declined to comment for this story, had had an eclectic career that veered from practicing personal injury law to operating a taxi fleet with his father-in-law. He ultimately functioned as both a Trump lawyer and shark-toothed loyalist.

He worked on some deal-making efforts but also spent much of his time threatening lawsuits, berating reporters and otherwise maneuvering to neutralize potential reputational dings for his boss, according to congressional testimony that Cohen gave after breaking with Trump in 2018. The rupture came after FBI raided Cohen’s home and office and Trump began to distance himself from the attorney.

Cohen soon told a federal court that he had helped candidate Trump wield the National Enquirer tabloid as a sort of house organ that flattered him, tried to flatten his opponents and bottled up seamy allegations about his personal life by buying stories or flagging them to Cohen to purchase. Trump says all the stories were false.

Those arrangements, which Manhattan District Attorney Alvin Bragg’s office portrays as a multipronged scheme to keep information from voters, are now under a microscope at Trump’s hush money trial. He has pleaded not guilty to 34 counts of falsifying business records so as to veil reimbursements to Cohen for paying off porn performer Stormy Daniels. She claimed a 2006 sexual encounter with the married Trump, which the former president has denied.

Other witnesses have testified about the hush money dealings, but Cohen remains key to piecing together a case that centers on how Trump’s company compensated him for his role in the Daniels payoff.

Trump’s defense maintains that Cohen was paid for legal work, not a cover-up, and that there was nothing illegal about the agreements he facilitated with Daniels and others.