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.