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.

(CNN) A new poll showing a majority of Americans think President Donald Trump is a racist reflects an unmitigated disaster for the nation -- it is a sad testament to Trump's fateful decision to draw political sustenance from the poisoned well of racial resentment.

A house divided against itself cannot stand, Abraham Lincoln said 160 years ago. It's no less true today: Our nation fails a little bit when some are scorned, ignored, cast out as perpetually inferior, inherently criminal and morally unworthy of help, respect and a hand up.

But from Lincoln's day to the present moment, there have always been politicians willing to stoke resentment and pander to fear and hatred. It is a simple, durable and reliable path to power.

Trump chose that path.

My friend Bill Moyers famously recounts an observation that his former boss, President Lyndon Johnson, made about cynical Southern segregationist politicians. "If you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket," Johnson said. "Hell, give him somebody to look down on, and he'll empty his pockets for you."

Trump has been a master of giving people somebody to look down on. Sitting on set at CNN in June 2015, I watched him on air announcing his candidacy with slurs against Mexicans. "They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people."

In December of that year, he called for "a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what the hell is going on."

But the core, crucial incitement by Trump -- one that signaled his intent to invent and exploit racial divisions -- was his allegiance to, and promotion of, the birther lie , a grotesque conspiracy theory that held that President Barack Obama was born in Africa and therefore ineligible to serve in the White House.

As The New York Times noted in September 2016, "it took Mr. Trump five years of dodging, winking and joking to surrender to reality, finally, on Friday, after a remarkable campaign of relentless deception that tried to undermine the legitimacy of the nation's first black president."

JUST WATCHED Democratic senator sounds off on Trump comment Replay More Videos ... MUST WATCH Democratic senator sounds off on Trump comment 01:56

Trump's birtherism was not an honest mistake but a cynical, thinly coded appeal to white resentment. Ditto for his scornful, dismissive campaign "appeal" to black voters -- delivered before white audiences: " What the hell do you have to lose?

More recently, when black professional athletes chose to protest police brutality by solemnly kneeling during the National Anthem, Trump -- right on cue -- shouted obscenities into the night at a rally in Alabama: "Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, to say, 'Get that son of a bitch off the field right now. He is fired. He's fired!' "

And in arguing against immigration from Haiti and African countries, he reportedly told a group of lawmakers he considered them "shithole countries," though he later denied doing so.

So it comes as no surprise that 49% of all Americans (65% of blacks) think race relations have grown worse during Trump's first year in office, according to one poll.

The great irony is that Trump, as a television celebrity, was remarkably popular with black and Latino audiences. At one point in 2000, according to Fortune magazine , in an "800-person survey conducted by Democratic pollster Rob Schroth, Trump scored a 67% favorable rating among blacks (vs. 21% unfavorable), 62% among Hispanics, and 66% among whites earning under $25,000."

Joshua Green, author of "Devil's Bargain," an analysis of Trump and his ex-adviser Steve Bannon, says, "(T)here was a moment in 2010 where Trump really could have run as a different kind of Republican candidate. ... But instead, Trump decided in 2010, 2011, to launch off on his birther rant which immediately plunged his favorability ratings with African-American voters, Hispanic voters soon followed, and he transformed into the hard-right, anti-immigrant politician that he is today."

As the nation approaches the 50th anniversary of the Rev. Martin Luther King Jr.'s assassination, we are more divided than we should be -- thanks in no small part to a President who chose to build his power on the quicksand of racial resentment rather than a firm foundation of tolerance.

And so, ironically, a man who began as a builder now presides over a house that is divided, tottering and at risk of collapse.

Leaders of his Republican Party -- who have maintained a cowed and shameful silence in the wake of Trump's outbursts -- should disavow the politics of resentment in this and every election year. Little by little, if more officials from the party of Lincoln summon the courage not to follow in his footsteps, voters can take back control from a President who is leading us down a dark and dangerous path.