>shall hold their Offices during good Behavior
"good behavior" for justices and "high crimes and misdemeanors" for the President both qualify the same exact procedure of impeachment; they are interchangeable. Presidents have to be good and justices have to obey fiduciary duty.
In other words Congress can impeach and remove for whatever reason it deems appropriate, just as the President can fire any of his subordinates at will regardless of any civil service laws.