A real debate would consist of policy experts from across the spectrum asking the candidates or their advisors to defend their policy proposals. Instead of a series of general questions, the debate questions would focus on specific flaws in the policies and try to determine what they do if things don't go as planned. It's important that the experts come from across the spectrum rather than involving people who are on the same basic side. A debate like that doesn't have to be a big production, especially if the candidates themselves don't take part and it's uploaded in video form to a video-sharing site with a transcript provided. In fact, that's something that The Nation could put on, if they want to see what a real debate is like. Details here.