Story highlights Ruth Ben-Ghiat: Trump's denunciation of anti-Semitism in interview is welcome, but late for a man who stoked bigotry throughout campaign

She says he should rid White House of alt-right influences, reject considering a plan that would limit terror probes to Muslim-linked acts

Ruth Ben-Ghiat is a frequent contributor to CNN Opinion, and professor of history and Italian studies at New York University. Her latest book is "Italian Fascism's Empire Cinema." The opinions expressed in this commentary are solely those of the author.

(CNN) "Anti-Semitism is horrible. And it's gonna stop and it has to stop," President Donald Trump announced Tuesday during a visit to the National Museum of African-American History and Culture. "You don't know where it's coming from but I hope they catch the people."

Many may feel relieved at this statement, which was occasioned by the latest evidence of a sharp uptick in anti-Semitism in our country. Just over the last few days, we've seen a slew of bomb threats to Jewish community centers around the country and the desecration of over 100 headstones at St. Louis' Jewish cemetery.

President Trump showed some leadership with this communication, but we can ask: Why did it take him so long to decide to acknowledge reality? Just last week, he disheartened many by telling a reporter from a Jewish newspaper that merely asking about anti-Semitism was "not a fair question."

And while it's true that as of now the perpetrators of these crimes have not been found, Trump's assertion that "you don't know where it's coming from" is disingenuous, since he has contributed to the rise of that anti-Semitism in multiple ways from the very start of his campaign for president.

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Trump long used powerful racist images to build his political brand and constituency during the race for the presidential nomination, setting himself up as the lone protector of white Christian America. In July 2015, his campaign released an ad that featured men dressed as Nazi SS soldiers with a message proclaiming that "We need leadership!"