As you will have seen in our documentation, since 2007 we have done polls after the election itself, and from those polls we see the degree of viewership. It's still a substantial viewership. The persons who are watching will attest to whether or not watching this particular debate or that particular debate contributed to their voting decisions later. A leadership debate will probably be the most important, but the others also factor into the voting decision.
On January 30th, 2018. See this statement in context.