No matter your views on President Donald J. Trump, the one decision he has made since taking office that is most likely to produce tangible positive results for the United States is the appointment of Lt. Gen. H.R. McMaster as his national security adviser. As bad as was Trump’s initial choice of Michael Flynn for that job — made even though the presidential transition team apparently knew that the retired lieutenant general was under investigation for lobbying on behalf of a foreign government — making McMaster Flynn’s replacement rectified a huge mistake. McMaster is the consummate soldier-scholar who has not been shy about espousing his unconventional views of the peculiar military-political relationship in this country and its sometimes deleterious impact on national security.