One idea would be to have the ex-Presidents on a video discuss what they thought about the position and its responsibilities. Then have them intersplice Trump's most ridiculous norm-breaking acts. So maybe showing each president laying wreath at the Tomb of the Unknown Soldier, then have John Kelly looking into the camera describing the notification of a parent like himself when a soldier dies, then have others describe how Trump didn't want to see wounded warriors or travel to the military cemeteries, then have the footage of the ex-presidents at McCain's funeral, then have the ex-presidents sitting on a porch talking about that sacred duty. Then end with John Kelly saying "My son wasn't a sucker"
But, that's just one idea.