Hunter Biden’s lead attorney defending him in a federal criminal investigation will stop representing him because he could be called as a witness in the case as plea negotiations broke down, according to a Tuesday morning court filing.

Christopher Clark, a high-profile litigator who has also defended big-name business people and celebrities like Elon Musk and Mark Cuban, has represented the president’s son throughout his legal troubles. Biden was set to enter a plea deal in federal court last month, but the agreement hit a roadblock after the judge questioned the potential immunity it would grant him.

Negotiations for a plea deal are now at an “impasse,” according to David Weiss, the prosecutor who has looked into Biden’s taxes for years. Attorney General Merrick Garland on Friday granted Weiss special counsel status.