The challenge in polarized political times is to keep your eye on democratic institutions and their proper authority. That’s the reason to applaud the nine House Republicans who voted last week to hold Steve Bannon, the sometime Donald Trump counselor, in contempt for defying a Congressional subpoena. The subpoena was issued by the special committee investigating the Jan. 6 Capitol riot, and there are no doubt some partisan motives at play. Speaker Nancy Pelosi hopes the committee will find evidence to back up her claim that the riot was part of a larger plot to stage an “insurrection.” If so, it was the dumbest coup attempt in history, but the committee wants to ask Mr. Bannon about his role.

Mr. Bannon’s claim of executive privilege has no legal merit. The Supreme Court has said the privilege applies to conversations with a President performing the responsibilities of his office or making policy or decisions. Mr. Bannon left the White House staff in the summer of 2017. He has no immunity as a private citizen who may have spoken with then President Trump.

The House voted to hold him in criminal contempt. Congress has referred the contempt citation to the Justice Department for possible criminal prosecution. The U.S. Attorney for the District of Columbia will have to decide whether to prosecute, and doing so would save Congress’s enforcement power from becoming a dead letter. That power has withered in recent decades.

Republicans held official Lois Lerner in contempt in their probe of IRS bias, but Justice never prosecuted. We count at least four times in recent years that Congress made criminal contempt referrals, and none was prosecuted. If Mr. Bannon becomes another, everyone will assume that Congressional subpoenas have no force.

One Member of Congress who seems to get this is Rep. Nancy Mace, the first-term Republican from Charleston, S.C. She voted against impeaching Mr. Trump twice. But she voted to hold Mr. Bannon in contempt on grounds that she wants a subpoena to mean something when Republicans are in the majority, as they could be as soon as 2023. Partisanship should matter less on this point than the preservation of Congress’s power to investigate issues and the executive branch. Congress also has its own inherent contempt power and could jail Mr. Bannon on its own until he testifies. Had the GOP taken that step against Ms. Lerner, the House special committee would be in a stronger position today.

Mr. Bannon has a Fifth Amendment right not to incriminate himself if he does testify. But he doesn’t have the right to defy a subpoena with impunity. President Biden blundered when he interfered with a prosecutorial decision by saying publicly that Justice should prosecute Mr. Bannon. Mr. Biden has since admitted his mistake.

Either Congress itself or Justice has good reason to vindicate Congress’s subpoena power under Article I. Republicans will be grateful when they’re back in power.

— Wall Street Journal