Donald Trump has spent the past few days excoriating National Football League players for “disrespecting” the country, the troops and the American flag. But not once, in his Friday night “get that son of a b***h off the field” speech, or his tweets questioning the patriotism of Colin Kaepernick and other professional athletes for kneeling during the playing of the national anthem, has the President addressed that as a candidate, he explicitly promised African-American voters that under his administration, “the law will be applied fairly, equally and without prejudice”.

Which is pretty much all that Kaepernick’s protest is about.

Clearly, Kaepernick and Trump do not, and will not, see eye to eye on issues of race and justice: Kaepernick once called Trump “openly racist”. Trump rejects the suggestion that his feud with NFL players, whose ranks are about 70 per cent black, has anything to do with race, even though he made sure to compare NFL patriotism with that of overwhelmingly white Nascar, and even though the underlying issue of the protests is police violence and the trust deficit between communities of colour and legal authorities.

It was only a few weeks ago that Trump tried to make light of the practice of protecting suspects’ heads when they are being put in the back of a police cruiser, telling a gathering of law enforcement officers, “You can take the hand away, OK?”

But at a point in Trump’s campaign when he decided it was necessary to at least signal that he wanted African-American support — his “what the hell do you have to lose” phase — he made a series of explicit appeals to the black electorate, including his October “new deal for black America” speech in Charlotte, Virginia, where he said:

“I have heard and listened to the concerns raised by African-American citizens about our justice system, and I promise that under a Trump administration the law will be applied fairly, equally and without prejudice. There will be only one set of rules — not a two-tiered system of justice.”

That is, exactly, the top-line demand of Kaepernick and, for that matter, Black Lives Matter. Trump also said:

“Every African-American citizen in this country is entitled to a government that puts their jobs, wages and security first. ... Here is the promise that I make to you: whether you vote for me or not, I will be your greatest champion.”

On patriotism and protest, Trump said:

“African-American citizens have sacrificed so much for this nation. They have fought and died in every war since the Revolution, and from the pews and the picket lines they have lifted up the conscience of our country in the long march for civil rights.”

This was, of course, scripted Trump, not off-the-cuff Trump. The speech was billed as a discussion of issues near and dear to African-Americans, even though the gathered audience was predominantly white. In the end, Trump got 8 per cent of the black vote and there were plenty of reasons to be sceptical about his commitment on issues of race: his role in amplifying birtherism, his remarks about Judge Gonzalo Curiel and his dismissal of Black Lives Matter as a movement “looking for trouble”.

Even Trump’s intermittent appeals to black voters were focused on the economy and jobs, not community-police relations. His idea of police reform is a ramped-up “law and order” posture, not scrutinising police for the string of widely publicised shooting deaths of unarmed African-Americans. Indeed, his Justice Department announced this month that it is reducing the role of the Office of Community Oriented Policing Services. Trump’s Attorney-General has pushed back on bipartisan sentencing reform efforts.

But that speech illustrates that Trump had no hesitation about trying to align himself with the aspirations of black America when it seemed advantageous to project the image of a president who would be there for all Americans. When you give a speech that takes a “two-tiered system of justice” as a fact of life and shout out black Americans who took to the “picket lines” and “lifted up the conscience” of America, you are acknowledging the vitality and patriotism of non-violent social protest.

The wrinkle is that Trump says a national anthem protest, specifically, is disrespectful. But he has not even attempted to engage with the explanation offered by Kaepernick’s former team-mate, Eric Reid, that he “chose to kneel because it’s a respectful gesture”, likening kneeling to “a flag flown at half-mast to mark a tragedy”.

By the end of last year’s election cycle, Americans were being counselled that the best way to interpret Trump was “seriously, but not literally”. How seriously, though, do you take a president who literally trash-talks citizens who are taking a knee to bring attention to the disparate administration of justice that Trump said he would fix?

To question the patriotism of athletes protesting to demand, in effect, that “the law will be applied fairly, equally and without prejudice” — the President’s own words — underscores just how hollow those words were.

• David Swerdlick is an assistant editor for The Washington Post’s opinion site PostEverything