This is a very important issue. There may be no graver danger to any country than a politicised military. The commitedly apolitical character of the U.S. military is its finest characteristic.
But that kind of institutional norm must be built and rebuilt, endlessly maintained, rather than taken for granted, as you have regular turnover in personnel, and now both new technology for sharing political ideas and increasingly sharp partisanship.
A most crucial point young military people just be, and are, taught is that they serve the country, not the President. Those who treat the President as the embodiment of America - something the Framers of the Constitution did not intend - increase the danger, especially those who are calling impeachment a coup.
Democrats are in no way blameless here. Their adoration of Obama is part and parcel of America's increasingly dangerous president-centric character. But because the military naturally leans conservative, the greatest danger comes from the Republican Party, and especially with a populist narcissistic President like Trump, who, like a cult-leader, is able to persuade people to follow him above everything else, unquestioningly, regardless of their ultimate doom.