Lawyers for Donald Trump asked a judge Thursday to dismiss the Washington federal election subversion case against him, arguing the Republican is immune from prosecution for actions they say were taken in his official role as president.

The motion amounts to the most pointed attack yet by defense lawyers on the federal case charging Trump with plotting to overturn the results of the 2020 presidential election he lost to Democrat Joe Biden. It tees up a fight over the scope of presidential power, forcing courts to wrestle with whether the actions Trump took in his failed bid to remain in office fell within his duties as commander-in-chief or whether they strayed far outside his White House responsibilities and are subject to prosecution.

“Breaking 234 years of precedent, the incumbent administration has charged President Trump for acts that lie not just within the ‘outer perimeter,’ but at the heart of his official responsibilities as President,” the defense motion states. “In doing so, the prosecution does not, and cannot, argue that President Trump’s efforts to ensure election integrity, and to advocate for the same, were outside the scope of his duties.”

The presidential immunity argument had been foreshadowed for weeks by defense lawyers as one of multiple challenges they intended to bring against the indictment.

Special counsel Jack Smith’s team is expected to vigorously contest the motion. It is not clear when U.S. District Judge Tanya Chutkan might rule, but potentially protracted arguments over the motion — including an expected appeal if she denies the request — could delay the case as courts step into what defense lawyers described an unsettled question.

The Supreme Court has held that presidents are immune from civil liability for actions related to their official duties. But Trump’s lawyers noted in their motion that no court has addressed the question of whether that immunity shields a president from criminal prosecution, hinting that the defense will likely fight the issue all the way to the nation’s highest court.