Dorothy A. Brown is a professor of law at Emory University. The views expressed in this commentary are solely those of the author. View more opinion articles on CNN.

(CNN) President Donald Trump is at it again, tweeting a thinly veiled racist attack ad designed to turn out his white base for the midterm elections. According to CNN exit polls 57% of white people voted for Trump in 2016. He needs them to come out and vote Tuesday to keep a Republican majority in Congress.

Dorothy A. Brown

The ad shows some frightening video of an undocumented immigrant from Mexico talking about killing police in the past and hopefully (he says, as he is led away by authorities) in the future. He smiles as he does this; his lawyer has said he is mentally ill.

The ad is designed to remind Trump voters of why they voted for him the first time. It is based on fear, not reality. The reality is those same white voters have more to fear from each other when it comes to crime than they do undocumented immigrants.

Recent Department of Justice statistics show that when whites are the victims of violent crimes, in 57% of the cases , the perpetrator is white. In other words, those 57% of Trump supporters should be looking at each other with more suspicion than they do at other racial or ethnic groups -- including undocumented immigrants.

The research is clear . Undocumented and legal immigrants are less likely to commit crimes than native-born American citizens. The libertarian Cato Institute published a study based on Texas data that showed native-born citizens are more likely to be convicted of committing violent crimes, such as homicide, than either undocumented or legal immigrants.

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