The Manhattan district attorney’s decision to sue key congressional Republicans to prevent one of his own rogue prosecutors from testifying on Capitol Hill signals a sharp escalation in the battle between Alvin Bragg and federal lawmakers over the indictment of President Trump.

The filing asks a federal judge to block the subpoena issued by the House Judiciary Committee chairman, Jim Jordan, and other Republicans to Mark Pomerantz, who quit Mr. Bragg’s office in frustration for what he perceived as the district attorney’s reluctance to charge Mr. Trump. He subsequently wrote a book, “People v. Donald Trump,” to air his complaints against Mr. Bragg’s stewardship of the case. 

Mr. Bragg’s suit calls Mr. Jordan’s subpoena a “brazen and unconstitutional attack” on his office and describes a “campaign of harassment in retaliation for the District Attorney’s investigation and prosecution of Mr. Trump,” who has been charged with 34 counts of falsifying business records.

The district attorney tells the court of an allegedly “transparent campaign to intimidate and attack District Attorney Bragg, making demands for confidential documents and testimony from the District Attorney himself as well as his current and former employees and officials.” 

Messrs. Bragg and Jordan have, in the past weeks, exchanged contentious letters, with the former defending his turf on federalism grounds. Here, the prosecutor claims that “Congress has no power to supervise state criminal prosecutions” and that “subpoenaing a former line prosecutor to talk about an ongoing criminal prosecution and investigation is no less of an affront to state sovereignty than subpoenaing the District Attorney himself.”

Mr. Bragg’s argument suggests that he sees himself, not Mr. Pomerantz, as the ultimate target of both congressional ire and Mr. Jordan’s subpoenas. Even this initial step, Mr. Bragg suggests, “threatens the sovereign powers of the States, confidence in the secrecy of grand jury proceedings, and the integrity of an ongoing criminal prosecution.”

Even as Mr. Bragg moves on Mr. Jordan, he tells the court that “Mr. Trump in particular has threatened New York officials with violent and racist vitriol,” indicating that the clash with his most prominent defendant is just getting under way. The filing also includes a picture from Truth Social showing the former president “threateningly wielding a baseball bat to District Attorney Bragg’s head.”

Rejecting the notion that Mr. Jordan is exercising his legislative duty of oversight, Mr. Bragg decries the lawmaker’s “baseless pretext for hauling Mr. Pomerantz to Washington for a retaliatory political circus designed to undermine the rule of law and New York’s police power.” 

The suit will be heard by Judge Mary Kay Vyskolcil, an appointee of Mr. Trump who previously ruled for the television host Tucker Carlson in a defamation suit brought by Karen McDougal, a former Playboy playmate who along with porn star Stormy Daniels is at the center of the hush money payments that precipitated the indictment.

Even as Mr. Bragg fights for his prosecutorial prerogative in court, the House Judiciary Committee, which Mr. Jordan heads, plans to hold a “field hearing” at Manhattan next week, to feature testimony of “victims of violent crime in Manhattan.” The event is meant to take place on the stomping ground of Democratic congressman Jerrold Nadler, the highest ranking member of his party on that body. 

Democrats, including Mr. Nadler, plan to hold their own press conference. The New York Democrat has promised that the “matter will play out in the New York criminal justice system, no matter how MAGA Republicans try to obstruct the process.”