They believe the African American vote will leave Trump? I don't think he was exactly counting on it.
Maybe 10% of 12% of the population is pretty insignificant. But I could also see the African American community looking around after white hooligans have burned down their housing, destroyed the ambulances they use, and leave their neighborhoods trashed deciding to vote for a leader who will lock up ANTIFA.
And also knowing the police cannot keep the peace, more guns are going to be sold in the upcoming weeks as home invasions increase.