“Taxpayers are paying a fortune for the use of Air Force One on the campaign trail by President Obama and Crooked Hillary. A total disgrace!” Trump tweeted Tuesday, hours before Clinton and Obama are scheduled to fly from Joint Base Andrews to Charlotte, North Carolina, for their first joint appearance.

Clinton is scheduled to address the National Education Association’s representative assembly Tuesday morning in Washington before the afternoon event.

Trump first raised the question Monday evening, tweeting, “Why is President Obama allowed to use Air Force One on the campaign trail with Crooked Hillary? She is flying with him tomorrow. Who pays?”

As conservative watchdog group Judicial Watch has uncovered, a typical trip aboard Air Force One costs upwards of $200,000 per hour.