Sen. J.D. Vance is calling for a criminal investigation into the judge overseeing Donald Trump’s hush money case in New York, citing violations of the former president’s First Amendment rights.

In a letter sent Wednesday to Attorney General Merrick Garland, Mr. Vance urged the Department of Justice to look into Judge Juan Merchan for his “illegal deprivation” of Mr. Trump’s freedom of speech by imposing a gag order, not dismissing prospective jurors who appeared “anti-Trump” and for barring evidence favorable to the former president

“On Merchan’s orders, a Republican presidential candidate has been made powerless to question the credibility of the witnesses testifying against him, the motivations of the prosecutors pursuing him, or the impartiality of the apparently conflicted judge fining him,” Mr. Vance, Ohio Republican, wrote. “That would be disfavored in the best of circumstances.”

Mr. Vance wrote that Judge Merchan “has not been content to deprive President Trump of only his First Amendment rights.”

The senator said the judge has also deprived Mr. Trump of a fair trial by an impartial jury, and listed different social media posts by two jurors on the case who showed their opinions on the former president.

“Another posted a video on social media showing her participation in an anti-Trump street demonstration,” Mr. Vance said of one of the jurors. “But Merchan was willing to impanel them anyway, forcing President Trump’s attorneys to burn critical peremptory strikes.”

The senator said Judge Merchan was “shameless” about the admission and exclusion of evidence, adding that he has “bent over backwards” for the prosecution but has used a “strong hand” against defense evidence.

In the letter, Mr. Vance mentioned the judge’s daughter, Loren Merchan, as “an obvious beneficiary of Merchan’s biased rulings.”

Ms. Merchan, a Democratic political consultant, was a hot topic for trial critics. Judge Merchan even had the gag order against the former president expanded to include his daughter and other family members because Mr. Trump kept railing against them on social media.

Mr. Vance said members of Manhattan District Attorney Alvin Bragg’s office have also been “plausible co-conspirators.”

“After all, they have repeatedly urged Merchan to deprive President Trump of his First Amendment rights in court filings and oral advocacy,” he wrote. “One can only wonder what sort of ex parte communications might have led Merchan to so enthusiastically embrace a prior restraint on speech that he would have known to be repugnant to the Constitution.”

Mr. Trump is facing 34 counts of falsifying business records in connection with hush money payments his former lawyer, Michael Cohen, says he made to adult film actress Stormy Daniels before the 2016 election.

The presumptive Republican presidential nominee and his supporters have railed against the case from the start, calling it election interference since his appearance in court keeps him from the campaign trail. Mr. Vance joined other Trump supporters in Congress in visiting the former president in the Manhattan courtroom this month in a show of solidarity.

The jury entered deliberation Wednesday after hearing closing arguments Tuesday.

• Mallory Wilson can be reached at mwilson@washingtontimes.com.