Jason Riley has this commentary in the WSJ.  Here are some excerpts.

President Obama is scheduled to speak in Dallas Tuesday at a memorial service for the five police officers gunned down last week--but haven't we already heard enough from him?

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Time and again during his presidency, in matters large and small, Mr. Obama has assumed the worst about police.

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Like others on the political left, Mr. Obama has made a habit of minimizing or ignoring the high black crime rates that obviously underlie tensions between poor minority communities and cops. More than 95% of black shooting deaths don't involve the police, which would seem to undercut the notion that trigger-happy cops are hunting black men. Sadly, rates of murder, rape, robbery, assault and other violent crimes are 7 to 10 times higher among blacks than among whites, but liberals who don't want to alienate black voters go to great lengths to explain away this behavior and focus instead on police conduct.

Yes, Mr. Obama has denounced what happened in Dallas, but he has also been winking at a Black Lives Matter movement that has spent the past two years holding rallies that call for (and sometimes feature) violence against cops. Like the president, these protesters maintain that the police are motivated by racial prejudice, not by the behavior of suspects. They insist that a biased criminal-justice system explains the black crime rate, not antisocial behavior. By indulging this narrative, Mr. Obama and his fans in the liberal media were playing with fire, and the Dallas carnage was the result.