Until this week, it was largely Mr. Cohen’s word against the president’s denials. That is why the admission by A.M.I. is “highly significant, because it goes to corroborate” Mr. Cohen’s testimony, said Jeff Tsai, part of the prosecution team that accused Senator John Edwards of campaign finance violations when he arranged for payoffs to a pregnant mistress during his 2008 presidential campaign.
“In any future prosecution, Mr. Cohen’s credibility is squarely at issue — as it should be — and that is where you see the nature of corroboration, either in the form of witnesses or documents, become such a pivotal factor in a prosecution,” Mr. Tsai said.
The Edwards case — which ended in an acquittal and mistrial — has been invoked by Trump allies as an example of prosecutorial overreach. Central to Mr. Edwards’s defense was that the payments were intended not to help his campaign but to hide the affair from his wife — that they were personal, not political.
Mr. Trump seemed to hint at this strategy in a tweet responding to Mr. Cohen’s admissions, in which he made an oblique reference to a “simple personal transaction” that was being wrongly called “a campaign contribution.”
Given the president’s stance, the disclosure of A.M.I.’s understanding that the efforts were campaign-related — and its promise of future cooperation — shows that potential witnesses against Mr. Trump go beyond Mr. Cohen.
Indeed, the A.M.I. agreement with prosecutors said there was at least one other person associated with Mr. Trump’s campaign involved in an initial discussion in August 2015, attended by Mr. Cohen and Mr. Pecker, in which they agreed that the publisher would help the campaign by identifying negative stories about Mr. Trump’s relationships with women “so they could be purchased and their publication avoided.”