Obviously you do not know much about the military, or about Trump.
The Dept. of Defense is the largest government department there is, and it is just as full of bureaucratic imbeciles and political hacks as any other department.
Officer above the grade of colonel are essentially politicians. This has been a known fact forever. While we admire and praise the bravery of fighting soldiers in the field, we despise political hacks in the Pentagon.
Bottom line, the Pentagon advice was crap and Trump did the right thing. The fighting men and women who lay their lives on the line know that their Commander in Chief has their back. And you charge, that Trump signaled to military personnel that he has the back of any military members who might disobey orders is just disgusting.