A group of two dozen Democratic members of Congress foreshadowed in a court case how they might fight back if President Donald Trump pardons someone for a criminal contempt of Congress charge — just as the two political branches ramp up the battle over congressional oversight.

House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., and Rep. Eric Swalwell, D-Calif., a member of the House leadership, were among the lawmakers who filed a brief last week to urge a federal appeals court in California to invalidate one of President Donald Trump’s most controversial pardons.

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Trump’s presidential pardon for Joseph Arpaio in 2017 allowed the former sheriff of Maricopa County in Arizona to escape punishment for a conviction of criminal contempt of court for disobeying a federal judge. And now the U.S. Court of Appeals for the 9th Circuit is reviewing a lower court’s decision not to vacate the conviction.

Nadler, Swalwell and the other Democratic members of Congress, in the brief, told the 9th Circuit that Trump’s pardon of a contempt of court charge infringed on the power of the judicial branch to impose sanctions for disobedience — just like a pardon of a contempt of Congress charge would infringe on the power of the legislative branch.

“A presidential pardon of contempt of court or of contempt of Congress is thus an encroachment on the independence of those co-equal branches of government,” the brief states.

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Trump’s pardon was done not to “ameliorate an unduly harsh criminal punishment or to correct a mistake in the enforcement of the criminal law,” the lawmakers argue, but instead to subject the authority of the federal courts “to the approval of the executive.”

The brief was filed as House Democrats take the first step toward holding Attorney General William Barr in contempt of Congress in their push to get an unredacted version of the special counsel report and its underlying investigative material on Russian interference in the 2016 election.

The issue is unlikely to rise anytime soon, even if the House votes to authorize legal proceedings against Barr or other people associated with the Trump administration. Any criminal contempt of Congress charges are all but certain to go nowhere with federal prosecutors, as long as Barr as the nation’s top law enforcement official.

But a new administration could decide to bring those contempt of Congress charges, so Trump could issue pardons before he leaves office to prevent those prosecutions, said former North Carolina Democratic Rep. Brad Miller, one of two lawyers who filed the brief on behalf of the lawmakers.

And Miller said there’s a pretty strong argument that the House could ask the federal courts to appoint a special prosecutor under the criminal contempt statute, since federal judges already can appoint private attorneys to prosecute contempt of court when government prosecutors decide not to.

“In the past, courts and Congress have had essentially the same contempt power,” Miller said.