I'd kill to be a fly on the wall in Marine HQ listening the commanders discuss how to navigate this bullshit.
On one hand, they have clear orders from the Commander in Chief. On the other hand, they know it's bullshit and anathema to the military's history and tradition. I'd like to think they'll show out and purposefully shove their collective thumbs up their ass.
In a perfect world, they would show up in casual uniforms and unarmed, just stand around lackadaisically. What perfect opportunity for malicious compliance!