I don’t think he’s rehearsing. I think he’s being interviewed and is stumbling over his words and the reporter is allowing him to get right what he wants to say. I say that because reporters have been “caught” doing this before. They do it to make the best video possible, of course, but are more than happy to allow those espousing liberal causes to “fix” their statements while they allow the gaffes of conservatives to go on the air as is.
I disagree. As an actor, I wouldn’t be surprised if the camera had panned down we would have seen him holding his sides in his hand.