WASHINGTON — The Army has launched an investigation after a drill sergeant posted a video on social media of soldiers being hazed under a MAGA flag, which is a violation of regulations prohibiting political activity in uniform and on federal property, the service said. Staff Sgt. Thomas Mitchell on Friday uploaded a video on TikTok showing a group of trainees performing pushups and burpees in full body armor under a banner that read, “This Is Ultra MAGA Country.” The video was later deleted. But Mitchell posted a second video showing the same soldiers exercising in the same location but with...