I thought this was an interesting observation, and I think it's true. They're actually afraid of him.
Part of it, of course, is the fear of saying anything negative about anybody with any African heritage, but I think they're also afraid individually of attracting negative attention from him.
He doesn't treat any of them very well - they are actually not allowed to sit in the same part of the plane, even though Bush and all other presidents used to let the press come and hang out with them while traveling, and he has incredibly few press conferences. Also, he was supposedly angered by what he perceived as questioning from one or two of them (back in the days when he had press conferences where they were allowed to ask questions that weren't pre-arranged and pre-approved) and eliminated them from the list of participants. I guess they're lucky that's all he did.
But I think they are afraid of him.
Yeah, I think you're right -- he's a bully, and they know it, and they've heard all the Chicago stories. And Rahm Emmanuel stories -- dead fish, screaming fits.