We never had a rule that you couldn't interrupt people in a political debate because most people running for the job understood how serious it is and while they did interrupt each other, it never became a huge problem the way it did this year.
Likewise we never had a rule saying candidates couldn't call each other names or make personal comments about their bodies or mannerisms. The thought never crossed anyone's mind because it was unthinkable that anyone running for this job would have so little respect for it.
But now we need rules. If we're going to have debates in the next round, there has to be a way to cut off a candidate that's taking more than his share of the time. And a way to switch off a candidate when they call the other candidate a name, or make a comment about their appearance. And take the camera off a candidate that's making gestures with his arms or face while another candidate is talking.
If the moderators don't plan for this in advance they are responsible for what comes next. It's not as if it isn't obvious now that we can't assume that the candidates will behave like reasonable adults. We have to assume they won't.