The promotion by President Trump of an assistant United States attorney, Danielle Sassoon, to acting United States attorney for the Southern District of New York could signal approval of her highest-profile conviction — that of a fallen crypto billionaire, Sam Bankman-Fried. 

Mr. Trump intends to nominate the former chairman of the Securities and Exchange Commission, Jay Clayton, to the post that Ms. Sassoon now holds temporarily. That appointment, though, will require confirmation by the Senate. Until that happens, Ms. Sassoon will run the country’s most prestigious collection of prosecutors. The previous United States attorney, Damian Williams, was an appointee of President Biden who first brought the case against Bankman-Fried. 

Ms. Sassoon, who attended Harvard College and Yale Law School and clerked for Justice Atonin Scalia, was the lead prosecutor on the team that secured seven fraud and conspiracy convictions against Bankman-Fried. The government persuaded a jury that the crypto prodigy stole more than $10 billion in customer funds by funneling money to an investment firm, Alameda Research, from his FTX exchange. Bankman-Fried controlled both. 

Bankman-Fried was sentenced by Judge Lewis Kaplan to 25 years in prison without the possibility of parole, a ruling that he has appealed. His lawyers write in their appeal that their client “was never presumed innocent. He was presumed guilty — before he was even charged. He was presumed guilty by the media. … He was presumed guilty by federal prosecutors eager for quick headlines. And he was presumed guilty by the judge.”

That request for a new trial before a new judge is now before the Second United States Appeals Circuit. Bankman-Fried argues that “FTX was never insolvent, and in fact had assets worth billions to repay its customers.” Ms. Sassoon cross-examined Bankman-Fried during his three days on the stand, colloquies that are widely thought to have damaged the defendant’s standing before the jury.

Among the questions Ms. Sassoon asked Bankman-Fried on the stand were, “Did you say in private, ‘F— regulators?’”; “Did you call some customers ‘dumb motherf—ers’? ” ; and, “Did you fly to the Super Bowl in a private plane?” Bankman-Fried argues that FTX’s law firm, Sullivan & Cromwell, worked improperly closely with prosecutors during FTX’s bankruptcy, for which the firm billed hundreds of millions of dollars. Sullivan & Cromwell declined to comment to the Sun.  

Ms. Sassoon also cross-examined the erstwhile head of Alameda Research, Caroline Ellison, who was also Bankman-Fried’s ex-girlfriend. Ellison eventually reached a cooperation agreement with prosecutors, and her guilty plea came with a two-year prison sentence. Ellison told Ms. Sassoon under oath that Bankman-Fried was “the one who set up the systems that allowed Alameda to take the money, and he was the one who directed us to take customer money to repay our loans.”

Bankman-Fried’s appeal argues that Judge Kaplan allowed Ms. Sassoon’s prosecution too much latitude in its effort to build the case against him. At one point during Ms. Sassoon’s cross-examination of Bankman-Fried, Judge Kaplan opined that “the witness has what I’ll call an interesting way of answering questions.” Bankman-Fried hopes that the riders of the Second Circuit detect prejudice in observations like that one.

Bankman-Fried was convicted of federal crimes, meaning that a presidential pardon, which covers all “offenses against the United States,” could be issued to him. The possibility of such a pardon, though, appears to have dimmed with the appointment of, in Ms. Sassoon, the woman who led the effort to convict him. 

A component of Ms. Sassoon’s case against Bankman-Fried was that he misused customer funds to make more than $100 million in political campaign contributions before the 2022 midterm elections. Most of that money went to Democrats, and Bankman-Fried was the second most generous individual donor to the party behind only the financier George Soros. Mr. Biden, though, did not issue Bankman-Fried a pardon.

Bankman-Fried last year told the podcaster Tiffany Fong that “all my Republican donations were dark. The reason was not for regulatory reasons, it’s because reporters freak the f— out if you donate to Republicans. They’re all super liberal, and I didn’t want to have that fight.” 

There could be some support for Bankman-Fried — or at least for crypto — in the new administration. Mr. Trump’s nominee to hold Mr. Clayton’s old job at the SEC, Paul Atkins, told a podcast last year that American regulations rather than any perfidy from Bankman-Fried were  to blame for FTX’s implosion. Mr. Trump, in his own way, is also involved with crypto. The president’s newly minted wealth from his $Trump meme coin is estimated, on paper at least, to be in the tens of billions of dollars.