WASHINGTON ― An advocacy group run by former government attorneys says President Donald Trump’s pardon of former Arizona sheriff Joe Arpaio is unconstitutional, and is urging a district court judge to refuse Arpaio’s request to vacate his contempt of court conviction.

Protect Democracy, a nonpartisan organization founded by alumni of the Obama administration, argued in an amicus brief on Monday that the president had overstepped his authority by pardoning Arpaio, who had endorsed Trump for president.

The brief comes the day the Department of Justice, led by Attorney General Jeff Sessions, sided with Arpaio in arguing that his conviction should be dismissed. DOJ attorneys wrote in a legal filing that because Trump had already pardoned Arpaio, “the government agrees that the Court should vacate all orders and dismiss the case as moot.”

That was something Protect Democracy anticipated ― its brief asks the court to appoint someone to argue against Arpaio’s request “in the event the DOJ does not vigorously pursue these arguments,” which now appears to be the case.

“The Arpaio Pardon does not faithfully execute the law; it sends a signal that public officials, so long as they are allies of the President, need not execute the law at all,” the filing reads. “The President cannot use the pardon power to invite other public officials to violate people’s constitutional rights.”

As sheriff of Maricopa County, Arizona, Arpaio prided himself on his efforts to drive out undocumented immigrants, and was found guilty of contempt of court in July for violating a court order from a 2011 racial profiling case.

Trump and Arpaio have been allies for years ― all the way back to when they both boosted the conspiracy theory that former President Barack Obama had lied about his birthplace. Pardoning Arpaio breached Trump’s duty to protect and defend the Constitution, the Protect Democracy filing argues.

The pardon power does not trump the rest of the Constitution. Protect Democracy

Trump announced Arpaio’s pardon on Aug. 25, as Hurricane Harvey bore down on Texas ― and later admitted he did so because he “assumed the ratings would be far higher.” He defended the pardon by saying Arpaio had “done a great job for the people of Arizona.”

U.S. District Judge Susan Bolton, who is overseeing Arpaio’s case, canceled his upcoming sentencing hearing. But she did not throw out the conviction ― instead, she set a hearing for Oct. 4 to hear arguments on whether she should vacate the charges, as Arpaio has requested.

Protect Democracy argues that Trump’s pardon of Arpaio represents “a severe threat to our constitutional order” because it violates three elements of the Constitution: the due process clause of the Fifth Amendment, presidential pardon authority under the Constitution, and the separation of powers.

The 2011 court order Arpaio violated was the result of a lawsuit brought by the American Civil Liberties Union and other groups. A judge presiding over that case ruled that it was unconstitutional to stop and detain drivers based on the suspicion that they were undocumented immigrants ― but Arpaio’s department continued the practice for months after the injunction anyway.

More than 170 people were wrongfully detained through racial profiling in Maricopa County in the roughly 18 months after the 2011 court ruling, according to federal prosecutors in the criminal contempt case.

“The President may no more use the pardon power to trample the rest of the Constitution and the Bill of Rights, than he may use the Commander-in-Chief power to call down airstrikes on political opponents,” the brief reads. “The pardon power does not trump the rest of the Constitution. The Arpaio Pardon seeks to do just that.”