The escalating confrontation between District Attorney Alvin Bragg and House Republicans suggests that an indictment of President Trump — which could happen any day — could open a rift not just between parties, but between federal and state government, exposing a nerve in America’s federalist system. 

The prosecution of a president by a local attorney has brought into focus the tensions crackling within the “dual-sovereign” structure created by the Founders. It’s a spectacle of the potential fingerprinting and mugshotting, by Gotham’s top prosecutor, of a man who once wielded the entire executive power of the United States. It threatens to not only upend a presidential race, but also make — or break — constitutional law.  

Mr. Bragg is under pressure from a troika of House Republicans, Jim Jordan, James Comer, and Bryan Steil. Over the weekend, they sent a second letter to Mr. Bragg decrying the “political pressure from left-wing activists” that they believe is driving the charges. They also accuse Mr. Bragg of “upgrading” misdemeanor charges against Mr. Trump even as he pursues — in routine cases — a policy of under prosecution. 

The congressmen aver that “this matter does not simply involve local or state interests,” but that the “potential criminal indictment of a former President of the United States by an elected local prosecutor of the opposing political party (and who will face the prospect of re-election) implicates substantial federal interests.” The parentheses and italics are in the original.

The trio of congressmen point to the possibility of a chilling effect, arguing that if “state or local prosecutors are able to engage in politically motivated prosecutions of Presidents of the United States (former or current) for personal acts, this could have a profound impact on how Presidents choose to exercise their powers while in office.”  

Messrs. Jordan, Comer, and Steil add that “any decision to prosecute a former or current President raises difficult questions concerning how to vindicate that interest in the context of a state or local criminal justice system.” No former president has ever been criminally charged by any federal or state authority.

Mr. Bragg’s office appears unconvinced, with the New York Post reporting that an employee answered a call from a House Judiciary staffer and announced, “Your committee has no jurisdiction over us. You’re wrong. Stop calling us with this bulls—.”

This missive comes on the heels of a letter from the same congressmen last week demanding communications, documents, and testimony relating to what they call Mr. Bragg’s “unprecedented abuse of prosecutorial authority” and deployment of a “novel legal theory untested anywhere” in a “zombie case” against Mr. Trump.

Mr. Bragg’s general counsel, Leslie Dubeck, argues in her own letter that the effort by these House Republicans is “an unprecedented inquiry into a pending local prosecution” and an incursion into “New York’s sovereignty.” 

Ms. Dubeck cites no less an authority than the Constitution’s 10th Amendment, which ordains that the “powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”

That clause has been read as guarding the sovereignty of states against what the philosopher Thomas Hobbes called the “Leviathan” of a centralized power, a reality the Founders knew all too well from their experience with the Crown. The Supreme Court notes that the “clearest example of traditional state authority is the punishment of local criminal activity.”  

The justices have, over the years, viewed this question not as one of dry technicality but rather as charged with the highest constitutional stakes, writing that the interference of the federal government in matters of local law enforcement “is peculiarly inconsistent with our federal framework.” 

Ms. Dubeck plants Mr. Bragg’s flag with particular conviction in the ground staked out in Younger v. Harris, an 8-to-1 decision handed down by the Warren Court in 1971 that held that federal courts may not interfere in pending state criminal prosecutions absent extraordinary circumstances. 

The majority opinion, by Justice Hugo Black, dilates on separated powers and observes that the “national Government will fare best if the States and their institutions are left free to perform their separate functions in their separate ways.”

In dissent, the longest-serving high court jurist ever — Justice William Douglas — writes that “whatever the balance of the pressures of localism and nationalism prior to the Civil War, they were fundamentally altered by the war. The Civil War Amendments made civil rights a national concern,” and thus empowered a more activist national government.  

The “Younger Abstention,” the principle that flows from this case, prescribes that the federal government stays its hand until state courts do their work — unless a law is “flagrantly and patently violative of express constitutional prohibitions in every clause, sentence and paragraph.”

Another case, Quinn v. United States, held in 1955 that Congress’s power to investigate “must not be confused with any of the powers of law enforcement; those powers are assigned under our Constitution to the Executive and the Judiciary.”  

The congressmen argue that their investigation of Mr. Bragg possesses a legitimate legislative purpose and could lead to lawmaking. They assert that “Congress retains broad authority to conduct oversight of ongoing civil and criminal investigations” in the name of “potential legislative reforms.” 

One of the areas for reform Messrs. Jordan, Comer, and Steil indicate an interest in pursuing is the authority “of special counsels and their relationships with other prosecuting entities,” given that the Stormy Daniels affair had its roots in the investigations of a special counsel, Robert Mueller.