From a political standpoint, however, what the president is doing is corrosively dangerous. He is impugning the character and competence of senior U.S. military leaders purely for political reasons. He is making clear that the “smart” generals and admirals are those who support him, and that “dumb” or “failed” officers are those who disagree with him. And he has no compunction about leveling blistering insults—in public—against some of America’s most highly respected military leaders.

Think of how far we have come—or how far we have fallen—from the days of the Cuban missile crisis, when John F. Kennedy called his predecessor, Dwight Eisenhower, for advice. Each man knew the importance of his rank and position; more to the point, they respected each other’s rank and position. Eisenhower, who was old enough to be JFK’s father, even called him “Mr. President” and “sir” in private. Kennedy, speaking to the man who had only recently sat behind his own desk, called Eisenhower “General.”

Yes, presidents have blown their stacks when hearing things they don’t like from their military advisers. (Lyndon Johnson supposedly unloaded on his service chiefs with such fury in a private meeting in 1965 that the chairman of the Joint Chiefs thought of resigning.) The Oval Office and the Pentagon are places where the survival not only of the country but also of the planet is decided, and tempers can run white-hot.

Read: The military has become Trump’s favorite prop

And, yes, retired military officers have not helped matters. Many of them have spoken out against Trump, in ways that would have been unthinkable even a decade ago. (It is important to remember that as recently as 1992, there was considerable tut-tutting about retired Admiral William Crowe’s endorsement of then-candidate Bill Clinton.) Retired generals including James Clapper, Mark Hertling, and Michael Hayden are regular critics of the president; even retired General Martin Dempsey’s Twitter feed, which never mentions Trump specifically, seems to be a continuing sub-tweet of the president, hashtagged under “#Leadership.”

But it is the president, not the generals and admirals, who have made this unthinkable situation part of the new normal in the Age of Trump. No modern president has been so reckless in his criticism of both active and retired military professionals. When Trump said he knew more than the generals—a laughable claim from almost any civilian when it comes to military affairs—he apparently meant it. And that means he has no respect for military advice, from any direction. This, more than any personal clash, was the clear message in Mattis’s resignation.

If Trump continues on this path—and he will—we could face the most politicized and divided military since Vietnam, or even since the Civil War. Generals and admirals could be faced with betraying their professional code either by giving the advice they know will keep them in the good graces of the president or by ignoring the president’s orders and protecting their troops in the field as they think best. The rank and file, meanwhile, will become accustomed to showing up at political rallies where their commander in chief will pander to them and air his grievances against other elected officials, all while they wave banners in uniform and cheer for a growing cult of personality.

I remain optimistic. The oath of the professional officer, like the oath of the federal servant, is to the Constitution. The men and women of the armed forces have withstood greater temptations than the empty praise and illusory bribes of a desperate president. But in civil-military affairs, as in so many other areas of our national security, we shall have much damage to repair before this business is over.