James B. Comey, the former F.B.I. director, asked a judge on Monday to throw out the indictment accusing him of threatening President Trump with a photograph of seashells arranged to read “86 47,” calling it a misuse of criminal law to punish free speech.

The charges, filed in North Carolina in April over an Instagram post Mr. Comey later deleted, say he “did knowingly and willfully make a threat to take the life of, and to inflict bodily harm upon, the president of the United States.”

Mr. Trump has argued that the term “86,” popular among restaurant workers, is mafia slang to kill someone, an accusation that many of his supporters have embraced. The other number, 47, is a reference to Mr. Trump, the 47th president.

“That claim,” Mr. Comey’s lawyers wrote in the new filing, “is contradicted by every possible source of meaning: dictionaries, context, precedent and common sense. ‘86’ simply means ‘get rid of’ or ‘eject’ and has no violent connotation except in the most uncommon usages.”

Mr. Comey’s lawyers are expected to file additional court papers on Tuesday, arguing that the case is part of a larger pattern of the Trump administration’s vindictive and selective prosecution of him.

Mr. Trump has publicly demanded that his Justice Department pursue criminal charges against Mr. Comey, whom the president blames for past investigations of his 2016 campaign and its possible ties to Russia as well as other conduct.

In September, Mr. Trump forced out a U.S. attorney in Virginia who concluded, along with career prosecutors, that the evidence did not support bringing charges against Mr. Comey over his testimony to Congress during a 2020 hearing. The president’s handpicked successor, Lindsey Halligan, a former insurance lawyer with no prior prosecutorial experience, then obtained an indictment against Mr. Comey, but the case was thrown out by a judge who determined that she had been unlawfully appointed.

Monday’s filing is focused on a narrower legal question, of whether the seashells photo constituted a true threat under federal law. Under a 2023 Supreme Court case, a true threat is a “serious expression” made by someone who intends to “commit an act of unlawful violence.”

The filing also notes that plenty of others, including protesters, right-wing activists and T-shirt vendors, have used the phrase “86” in reference to political figures, and have not been charged with threatening physical violence.

In a case involving demonstrators in Washington flying a flag reading “8647,” a federal judge concluded last month that “no reasonable observer could have viewed” the act as “a threat to the president’s life or physical safety.”