Trump uses the Military when it's convenient to him. We know how he feels about captured vets and Gold Star families if they don't agree with him. It's up to the NFL to decide what to do about the protests, but anyone who listened to these athletes know it's not against American flag or veterans.
That said, if NFL won't let Tebow promote God, or others wear Pink for breast cancer, then protesting against police brutality and racism should not be allowed either. Either let everyone use that platform to voice their beliefs or don't. You shouldn't get to pick or choose which ones you like.