Mr. Trump has managed to unite the players and owners against him, though several owners supported him for President and donated to his inaugural. The owners were almost obliged to defend their sport, even if their complaints that Mr. Trump was “divisive” ignored the divisive acts by Mr. Kaepernick and his media allies that injected politics into football in the first place.

Americans don’t begrudge athletes their free-speech rights—see the popularity of Charles Barkley —but disrespecting the national anthem puts partisanship above a symbol of nationhood that thousands have died for. Players who chose to kneel shouldn’t be surprised that fans around the country booed them on Sunday. This is the patriotic sentiment that they are helping Mr. Trump exploit for what he no doubt thinks is his own political advantage.