Editor’s Note: This article is one of 50 in a series about Trump's first two years as president.

Armed white terrorists, many of them Confederate veterans, stormed the July 1866 constitutional convention in New Orleans and slaughtered nearly 50 people, many of them black Union veterans. The attendees at the convention had committed a crime of dire proportions: They had sought to enfranchise the black population of Louisiana following the imposition of the Black Codes, laws that had reduced the black population of the state to a position of near-slavery. The white men of the South had no choice but to engage in mass murder.

Or at least that’s how the president of the United States saw it. “When they had established their government and extended universal or impartial franchise, as they called it, to this colored population, then this radical Congress was to determine that a government established on Negro votes was to be the government of Louisiana,” President Andrew Johnson told a supportive crowd in St. Louis in September 1866. “So much for the New Orleans riot—and there was the cause of the origin of the blood that was shed. And every drop of blood that was shed is upon their skirts, and they are responsible for it.”

Adam Serwer: The white nationalists are winning

Until the 20th century, most American presidents supported white supremacy, a ruling doctrine of the United States for most of its existence. Still, few endorsed mob violence or defended those who engaged in it. Until Donald Trump, who, in the aftermath of a white-nationalist rally in Charlottesville, Virginia, that led to the death of the counterprotester Heather Heyer, defended the racist marchers, saying that there were “very fine people on both sides.” Although it was a logical extension of Trump’s governing philosophy, the core of which is the preservation of America’s traditional hierarchies of race and gender, the statement nevertheless shocked a polity that has grown used to presidents who embrace pluralism, at least rhetorically.