Listen specifically at 1:11 of the video.
He is not asked if he disavows the KKK. I just listened again. Such a question is not asked at all.
He says he doesn’t know anything about David Duke.
Apparently, he doesn’t trust that talking head on anything and wants to check it out himself.
David Duke is hired to endorse people. I assume Rubio, Cruz, the establishment, the Barbors, or the Clintons made that hire.