Story highlights Joseph J. Ellis: Trump's Charlottesville remarks have inadvertently added two big things to our national conversation about race

The "again" in "Make America Great Again" is further back than we realized -- and we're all thinking more about American history

Joseph J. Ellis is the author of many works of American history, including the Pulitzer Prize winner "Founding Brothers: The Revolutionary Generation" and "American Sphinx: The Character of Thomas Jefferson," which won the National Book Award. He is the author of the forthcoming book "American Dialogue: The Founders and Us." The opinions expressed in this commentary are solely his.

(CNN) Donald Trump's controversial remarks in the wake of the Charlottesville riots have inadvertently made two significant contributions to our national conversation about race.

Joseph Ellis

First, Trump has for the first time clarified what "Again" means in his campaign slogan "Make American Great Again." It means before Brown v. Board of Education and the civil rights movement, somewhere around 1950. There had been dog whistles during the campaign to that effect, but he has now sounded his bugle, welcoming white supremacists and Jew-haters back into the political mainstream.

This make perfect sense once you think about it. For these "deplorables," as Hillary Clinton correctly called them, were always among the most visible participants at his campaign rallies. And they remain a vocal part of the nucleus of his political base. The most shocking fact about Trump's recent remarks is that we were shocked.

After all, Trump achieved credibility as a presidential candidate with the birther lie about Barack Obama, a blatantly racist claim he successfully lifted from the fringes of Breitbart to the mainstream of Fox News. And it worked for him.

White supremacists and Nazi sympathizers helped make both his nomination and election possible. Without them, and an even larger group of fellow travelers who share their racial prejudices less conspicuously, the Trump presidency might not exist.

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