I think he made it very clear as to what the military response would be if Trump ordered an invasion of Canada. The military pledges allegiance to the Constitution, not to the POTUS. He can only grant immunity to offenses against the United States. Murder is prosecuted at the state level. He can not offer blanket immunity in any case,and he cannot grant immunity 'going forward'. This officer of the American armed forces has obviously done his due diligence, and has made a statement based on sound facts. He chose his wording carefully. Trump can not issue a legal order to attack Canada, and the officers collectively will refuse to follow an order that is not legal. End of discussion, as he made clear. Trump has obviously been made aware of that, given his concerns that the issue has become 'overly emotional'.