A federal judge overseeing the criminal case of President Trump’s former national security adviser Michael T. Flynn opened the door late Tuesday for legal experts and other outside parties to oppose the Justice Department’s motion to drop the case, suggesting he has at least some skepticism about the government’s argument that Mr. Flynn should never have been charged.

In a brief order, Judge Emmet G. Sullivan of the United States District Court for the District of Columbia said he would set a schedule for outside parties to present arguments about the government’s request to dismiss the case. He did not directly address the Justice Department’s motion to drop the charge, but legal experts said he appeared open to considering not only the department’s arguments but also those who have challenged its move as politically motivated.