I think the white supremacist angle was just his derp talking point. Its obviously not true, but its in the script.
Derps gonna derp.
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Actually when I listened to the first press conference, it was a reporter who first suggested it, by asking if any of the outside agitators were white supremacists. The reply was a half hearted yeh some of them likely were-words to that effect.
Derp/Clown/Journal-list talking point.