“Nothing I’m saying now is new,” Cohen, 56, said in an interview. “The only difference is that this potential indictment will force the exposure of all of that information.”

Federal prosecutors ultimately decided not to act against Trump. The former president, who is running for a second term in 2024, has said that shows he is blameless, and has called all the cases facing him political vendettas.

Now Bragg appears to be on the verge of giving new life to the hush money case, with likely criminal charges such as falsifying business records and breaking campaign finance law – and with Cohen at stage centre.

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“He is an extremely problematic witness,” Rebecca Roiphe, a former prosecutor in the DA’s office who now teaches at New York Law School, said of Cohen’s criminal record. In addition to pleading guilty to campaign finance violations over the Stormy Daniels payment, he admitted to tax crimes and to perjury for lying to Congress about the timeline of discussions about a Trump Tower project in Moscow.

“But there are things that cut the other way,” Roiphe said. She noted that Cohen has already been sentenced and served his time.

“He doesn’t stand to gain here, unlike others who testify for a reduced sentence,” she said. “There is no get-out-of-jail-free card.”

She added that prosecutors would present corroborating evidence for anything important Cohen says on the stand.

“We’ve seen the cheques,” Roiphe said, referring to evidence of Cohen’s reimbursement.

Daniel Horwitz, formerly with the Manhattan DA’s office, agrees Cohen could be dangerous to Trump on the stand.

“Insiders come with baggage,” he said with a touch of understatement as he cited Salvatore “the Bull” Gravano, the mob underboss who admitted participating in 19 murders. Gravano was sentenced leniently for his testimony against bigger organised crime targets.

“People like Michael Cohen and Sammy the Bull had a front-row seat as to what the criminal conduct was,” Horwitz said. “Who better to give testimony?”

Bragg’s office declined to comment on the case. Trump spokesman Steven Cheung didn’t immediately respond to a request for comment on the investigation or Cohen’s role in it.

Cohen spent two days last week testifying before the grand jury Bragg convened, reviewing evidence of alleged crimes by Trump. But he has spent years going after his former boss in interviews, two tell-all books and a podcast.

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He famously warned Congress before the 2020 election that he feared Trump wouldn’t commit to a peaceful transition of power.

Robert Costello, a lawyer who said he once advised Cohen, said he testified on Monday for about two hours before the state grand jury investigating Trump as a rebuttal witness for the defence. Cohen denies Costello ever represented him.

Costello said he’d offered material about Cohen that he’d compiled in 2018 and 2019, which Costello said would show that Cohen is “totally unreliable.”

But of the 321 emails he’d handed over, the district attorney’s office “cherry-picked six emails to ask me about,” Costello said. “Of course, they took them out of context,” Costello said, adding that he’d urged the grand jurors to “ask for the entire packet” of emails, “which follow in chronological fashion and give you the life history of Michael Cohen”.

As recently as a year ago, Bragg appears to have balked at pursuing the payoff case. Mark Pomerantz, a former prosecutor with the Manhattan DA’s office who quit last year and published a book criticising Bragg for not pursuing Trump aggressively enough, said in the book that the DA told subordinates he “could not see a world” in which he would rely on Cohen as the foundational witness in a case against Trump.

All that has changed in the last two months, as high-profile potential witnesses including former top Trump aide Kellyanne Conway and Trump Organization Controller Jeffrey McConney have flowed in and out of Bragg’s offices.

Cohen and his lawyer, Lanny Davis, have been the most frequent visitors. Cohen says he has met with prosecutors 20 times.

Mark Bederow, a former assistant Manhattan DA now in private practice, warned of relying on Cohen.

“If this case is predicated on the testimony of Michael Cohen primarily, that’s a huge problem,” Bederow said. “Cohen has all the indicia of a bad witness. He’s an admitted liar, a convicted felon and has admitted personal animus against Donald Trump. To a defence lawyer, he checks every box as to being a terrible witness.”

The Justice Department has a long-standing policy against charging a sitting president, and federal prosecutors have previously expressed concerns about Cohen’s credibility. At his sentencing, they criticised his less than full cooperation in their investigation. They later decided against recommending a reduced prison term.

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“I acknowledged guilt under Section 1001 of the criminal code, by telling a lie to Congress,” Cohen said in the interview. “But I did it at the direction of, and for the benefit of, Donald J. Trump.”

He says his lie about the failed real estate project in Moscow paled beside more important, truthful testimony he has given, to Special Counsel Robert Mueller over Russian interference in the 2016 election, for example.

One key Republican talking point has been the “weaponising” of institutions against Trump and conservatives. On Saturday morning Trump posted on his Truth Social platform that “illegal leaks from a corrupt & highly political Manhattan district attorney’s office” indicated that he would soon be arrested, “with no crime being able to be proven”.

Cohen said the shoe is on the other foot – Trump’s.

“Over the past five years,” he said, “what we have seen exposed is the corruption and weaponisation of the Justice Department by an autocratic wannabe.”