I reject the premise. You don't have to be a white supremacist to attend a white supremacist event any more than you have to be Bronie to wander into My Little Pony convention or be a feminist to attend a feminist speech. He has nothing to apologize or make excuses for.
Agreed. The part where it is complete bullshit is
he was one of the fucking speakers for the rally. A bit hard to plead ignorance if you say into a microphone that you support the rally and its values.
That depends on the invitation and the actual speech he made.
They may have underplayed the nature of the event, and their values. "Our civic group is holding a convention, we expect 2000 people. Could you come and talk for 20 minutes about immigration (or whatever)."
The car picks him up at the airport, delivers him to the rally at 7:10, he's on stage at 7:15, back to the airport by 8:00. MAYBE no idea what he just endorsed with generic "Glad to be hear" noises made while promoting his own agenda to an audience.
Maybe. I mean, it's a possibility.
If he was the keynote speaker, or had anything to do with organizing it, of course, then this scenario is completely impossible.
On the other hand, if he's TRYING to distance himself from the Alt-Right, then he really DOES need to apologize. If he did not mean to be at such an event, he needs to make a distinct statement that it was a mistake, that he or his people need to vet events more stringently, that he does not condone, etc. It's not enough to say his presence was passive, not if he's trying to take a specific stance.
Looks, though, like he's trying to have it both ways. Appeal to the non-alt-right without offending the alt-right.