Errol Louis is the host of "Inside City Hall," a nightly political show on NY1, a New York all-news channel. The opinions expressed in this commentary are his own. View more opinion articles on CNN.

(CNN) It's not your imagination: President Trump, who regularly makes a point of personally insulting public figures who challenge or displease him in any way, taps into an especially toxic well of vitriol when aiming his attacks at black Americans.

This week alone, Trump berated CNN correspondent Abby Phillip ("What a stupid question. But I watch you a lot. You ask a lot of stupid questions.") He said of April Ryan , a reporter and CNN contributor who has covered the White House for 21 years: "You talk about somebody that's a loser. She doesn't know what the hell she's doing."

And at a post-election press conference, when Yamiche Alcindor of "PBS NewsHour" began to ask about accusations that his rhetoric may have emboldened violent white nationalist groups, Trump interrupted with, "I don't know why you say that. That is such a racist question."

The three women -- all of them gifted, accomplished professionals -- will be covering politics long after Trump has left the White House. They join a long list of athletes, entertainers, journalists and politicians who Trump routinely attacks as "dumb," "not qualified" or some such insult.

None of this is subtle or secret; that would defeat the purpose. For Trump, loudly and publicly denigrating black figures is the whole point.

He is a classic example of a backlash politician: a leader who exploits real or perceived white anxieties by exhibiting a flamboyant hostility to the political and economic demands of black Americans. We've had a string of such politicians since the civil rights movement, and that is neither surprising nor coincidental: Like many social revolutions, America's expansion of civil rights in the 1960s and '70s gave rise to a potent counterrevolution.

We saw it in Ronald Reagan's decision to launch his 1980 campaign for president at the Neshoba County Fair in Philadelphia, Mississippi, where an infamous triple murder of civil rights organizers had occurred in 1964. Reagan didn't mention the martyred civil rights workers Andrew Goodman, Michael Schwerner or James Chaney in his speech, which was all about state's rights.

As columnist Bob Herbert later noted: "Everybody watching the 1980 campaign knew what Reagan was signaling at the fair. Whites and blacks, Democrats and Republicans — they all knew. The news media knew. The race haters and the people appalled by racial hatred knew. And Reagan knew. He was tapping out the code."

Candidate Reagan, who had opposed the Civil Rights Act of 1964, went on to become President Reagan, who tried to weaken the Voting Rights Act and fought against making the birthday of Martin Luther King Jr. a federal holiday.

Trump knows the code. The prelude to his presidential run was his gleeful hyping of birtherism, a multiyear campaign of conspiracy theories and obvious lies that served no purpose beyond calling into question the legitimacy of Barack Obama's presidency.

Trump has never renounced, or even acknowledged, the obvious racism of his birther falsehoods, and he never will. Birtherism -- like talking about state's rights in Mississippi -- was a quick, convenient way to attract people ready to push back against black advancement.

"There was a shocking amount of resentment that a black family had been in the White House for two terms. I think it would be naive to overlook it — the irony that one of the legacies of Obama's presidency was an enormous amount of resentment," Harvard historian Henry Louis Gates said after the 2016 election. "I don't think a Donald Trump could have emerged without a black president. Donald Trump tapped into and fueled and stoked an enormous amount of racial resentment. And Obama symbolized it."

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With Obama no longer in the public spotlight, Trump has to play backlash politics with whatever black targets of opportunity happen to be around. That is why he never misses a chance to attack Rep. Maxine Waters, Don Lemon of CNN or the black reporters in the White House press corps.

It's a disgusting and dangerous business: April Ryan has been subjected to death threats in the wake of Trump's verbal attacks. One can only hope the fever breaks soon, with the public signaling to political leaders that dividing and denigrating people is no way to lead a great nation.