The problem is....he might be a speaker at both conventions.
That thought had crossed my mind as well.
However, I just can't see that happening. He might be tempted to accept invites to both conventions to try and play both sides of the fence, but the Dims will force him to choose one side or the other. They'd yank his invitation and instruct their propagandists to turn on him if he also accepts a speaking engagement with the Republicans.