Army General Mark Milley, chairman of the Joint Chiefs of Staff, had a tenure marked by a relentless series of challenges. He served through the U.S. withdrawal of forces from Afghanistan, Russia's invasion of Ukraine and rising tensions with China. He also served under an American president with little regard for the norms that have historically separated politics from the U.S. military: Donald Trump.In an interview shortly before his retirement last weekend, NPR's Mary Louise Kelly asked Milley about the relationship between the military and the executive branch — and how it was tested under Trump.Email us at considerthis@npr.org.