Notice that he starts with "I've written an entire book on what he [Jesus] said and did, ....(laughter) and for him to say and do anything, he had to exist."
So Bart starts from a biased point of view with some credibility to lose. That's similar to priests and JW's not being willing to entertain the idea that they could be wrong in their world view because they are invested in it.
He then dismisses anyone who writes a book suggesting that Jesus doesn't exist as not a serious scholar, but just someone who wants to make money writing a sensationalist story. Doesn't that sound familiar too?
There are good debaters and Bart is one of them. This host is not bad, but is not up at all on the subject, he is just a guy who hears what people say. If a financial expert disagrees with Steve Harvey about the financial stability of the dollar and an expert on botany disagrees with Ellen Degeneres about how to water cactuses, does that prove that the experts are correct? NO, it proves that they know much more about the subject than the talk show hosts they talk with.
Evidence for Jesus outside of the doctrinal writings is very slim. He may or may not have existed. It is highly possible that he is a composite of others.
Bart admits he has no personal investment in "Paul." That seems to indicate that he admits to his personal investment in Jesus. On the subject of Paul, it is highly more established that he did exist and wrote some of what is credited to him. But reading what experts are sure of, Paul's Jesus is a very mythical figure and Paul does not help to establish a real person in a real timeline. Even if Paul's existence is established, using anything he did or wrote to help establish Jesus would be like using the writings of the miraculous events surrounding Siddhartha Gautama to prove these things happened in the establishing of the Buddha.