I have known President Trump personally since 1986. The private Trump I have known is funny, charming and embracing. That is not the public Trump of today. When he loudly called for four members of Congress – women of color who oppose nearly all his initiatives and who have questioned his fitness for office – to go back to the places from which they came, he unleashed a torrent of hatred.

The "Go back" trope was used by white racists toward African-Americans for 100 years, from Reconstruction to the civil rights era, suggesting repulsively that they should go "back" to Africa; never mind their American births. It was uttered by the establishment at my grandfathers and many others who came here from southern Europe as children in the early days of the last century.

"Go back" is a rejection of the nation as a melting pot; a condemnation of one of America's founding values – E Pluribus Unum (Out of many, one). It implicates a racial or nativist superiority: We were here before you; this is our land, not yours; get out. Nativist hatred is an implication of moral or even legal superiority that has no constitutional justification in American government.

Don't get me wrong. Even though hate speech – speech that expresses hatred for people, as opposed to hatred for ideas – stings and hurts, it is constitutionally protected. The remedy for hate speech is not to silence the hater but to shame him. And the most effective way to do that is with more speech.

But when the hate speech comes from a shameless president, we have a problem.

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The problem is that presidential hatred produces division among people and destroys peaceful dialogue. When thousands of people at a Trump rally in North Carolina recently chanted, "Send her back" referring to a congresswoman born in Somalia – and Trump tweeted that the four congresswomen (including three born in the U.S.) should "Go back" to where they came from – the inescapable image was of a president trying to divide rather than unite.

At first, Trump seemed to welcome the chants. Then, two days later, he distanced himself from those who chanted. Then, three days after that, he praised the chanters.