One of the President's religious advisers, the Texas pastor Robert Jeffress, brought the ghosts of the old South flooding back. Jeffress said: "They [the NFL players] live in a country where they're not only free to earn millions of dollars every year, but they're also free from the worry of being shot in the head for taking a knee like they would be if they were in North Korea."
When Stevie Wonder went down on one knee before a concert in Central Park, Congressman Joe Walsh tweeted that he was "another ungrateful black multi-millionaire".
Not getting "shot in the head" is largely what this is about.
All serious American historians agree that race is the central unresolved issue of America's development as a nation. The end of the Civil War brought a victory for one side, but not a settlement. Resentment in the southern states continued to fester and gave rise to the growth of the Ku Klux Klan in the 1920s, while segregation endured until the Civil Rights Act of 1964.
Inequality, the mass incarceration of young black males, and police shootings, are seen by many as the next episode in that national story, and explain the feelings that just happened to find an outlet through Kaepernick and the NFL. Black males between 15-34 are nine times more likely to be killed by law enforcement officers than other Americans.
As the debate raged after this week's protests, which are spreading across American sport, Kaepernick's teammate, Eric Reid, told the New York Times why he became involved.
"In early 2016, I began paying attention to reports about the incredible number of unarmed black people being killed by the police," Reid wrote. "The posts on social media deeply disturbed me, but one in particular brought me to tears: the killing of Alton Sterling in my hometown Baton Rouge.
"This could have happened to any of my family members who still live in the area. I felt furious, hurt and hopeless. I wanted to do something, but didn't know what or how to do it. All I knew for sure is that I wanted it to be as respectful as possible. A few weeks later, during pre-season, my teammate Colin Kaepernick chose to sit on the bench during the national anthem to protest police brutality.
"I have too often seen our efforts belittled with statements like 'He [the victim of a shooting] should have listened to the officer,' after watching an unarmed black person get shot, or 'There is no such thing as white privilege' and 'Racism ended years ago.' We know that racism and white privilege are both very much alive today."
Last year, Trump told Kaepernick to "find a country that works better for him." He also claims his son-of-a-bitch remark had "nothing do to with race." Kaepernick meanwhile also needs to find a job, because NFL franchises have turned their back on him.
In one week a private protest has flared into a debate about America's purpose and meaning under Trump, with Steve Kerr, the head coach of basketball's Golden State Warriors, declaring: "Nationalists are saying, 'You're disrespecting our flag.' Well, you know what else is disrespectful to our flag? Racism. And one's way worse than the other."
Jim Caldwell, coach of the NFL's Detroit Lions, also defended the demonstrators: "There are no SOBs in this league. These are men that work hard, of integrity, they're involved in our communities. They're fathers, they're brothers, and their mothers aren't what [Trump] said they were. And our guys believe in unity, civility, and also the First Amendment rights to peaceful expression and freedom of speech."
In Sports Illustrated, players queued to say this was not a rejection of America's core institutions or values.
"It has nothing to do with our military," said Kenny Vaquero of the New Orleans Saints. "One of my best friends served three terms in Iraq. I don't think it's a fight against Trump. I think we need to focus on the real problem. The inequality, the police brutality - that's the real problem."
The Trump presidency is being acted out on many battlefields. But historians may yet trace its end in part to the time he set out to stigmatise athletes whose prime objective was to stop others from their communities being shot through the windows of cars by police officers routinely excused by the justice system. By whipping up his own constituency, on the gridiron field, Trump is uniting the saner, more compassionate America he seeks to destroy.