To be clear, Gen. Milley is perfectly within his rights to disagree with the president — behind closed doors. But the moment he takes his disagreement and goes public on his own authority, as Truman said of MacArthur, this is “open defiance” of a president’s orders.

What is notable, in sum, is that on two separate occasions Gen. Milley has openly challenged the Constitution.

First by criticizing the president for standing up for religious liberty — as enshrined in the Constitution — with the presidential visit to a church burned quite deliberately by “protesters” who were in fact would-be arsonists.

Second is the general’s open public statement that is effectively issued, in Truman’s phrase, in “open defiance” of his president and commander-in-chief.

To which, the answer to Gen. Milley is the obvious one. If the general can’t obey the Constitution — he should resign.