He took it down shortly after and one excuse I heard put forward is that trump simply didn't listen to the whole content of the video and sent it out as soon as he heard support for himself. Call me paranoid but I wouldn't doubt he knew exactly what the whole content amounted to and aired it anyway as a quick reminder to his base, then removed it with a wink and a nod. I have no douibt he's a racist.
It's totally believable that he didn't watch the video.
He usually doesn't take anything down. Had he posted a White Power video on purpose, I don't think he'd have taken it down.
Either way, it's either racism or incompetence.