The Republican candidate for governor of Pennsylvania posed for a picture wearing a Confederate uniform while an instructor at the US Army War College, according to a report.
Mastriano, a retired Army colonel and military historian, posed for a photo with other faculty members who were given the option of dressing in historical garb. Six of the instructors did so.
Mastriano did not respond to a request for comment.
The Department of Defense banned Confederate flags from bases in 2020.
The point person for the former president's campaign in its effort to overturn the 2020 election in Pennsylvania has been Mastriano. According to The New York Times, he had to be reassured that his role in the plot wasn't illegal.
The governor candidate faced criticism over his efforts to cultivate support on the social network founded by a self-proclaimed Christian nationalist.
Mastriano paid the network $5,000 for consulting services before he deleted his account. The founder of Gab contemptuously stated that Jews have no place in his right-wing movement.
It's a sensitive issue in Pennsylvania. The Tree of Life synagogue in Pittsburgh was the site of a massacre in which 11 Jews were killed.
Gettysburg is the site of the bloodiest battle of the Civil War, which the Union side won.