WASHINGTON — A photograph of President Trump and his top four-star generals and admirals, tweeted in October by Defense Secretary Mark T. Esper, was meant as a thank-you to the commander in chief. But it angered a lot of others, and not just those who erupted on Twitter. “You would have thought it was 1950,” said Lt. Col. Walter J. Smiley Jr., who is African-American and fought in Iraq and Afghanistan before retiring last year after 25 years in the Army. Dana Pittard, a retired major general, also African-American, was equally frustrated. “It’s America’s military,” he said. “Why doesn’t this...