This is not about disrespecting the anthem, or the flag, or soldiers.
It was a simple protest against black inequality in the criminal justice system.
Trump, in his evil-genius way, has exploited the protest for his own political ends -- insinuating that black athletes (the NFL majority) are disrespecting things his white voters (the majority of fans) believe in, ie the flag, soldiers etc. His flag-waving base eats this stuff up. It's like pouring gas on a fire.
Of course, it is dog whistle politics from The Master himself:  "You, my white working class voters should not take this dishonour from these spoiled, millionaire black athletes."
The Master Manipulator has once again whipped the country into a frenzy over a minor expressive act -- after all how insulting can dropping to one knee really be?