Unless the guy is planning to leave you a lot of money or you work directly for him why didn’t you just tell him to “eff off”? It would have been short, sweet and allowed you a lot of extra time to do something else like drink a beer.
It could come to that, but I do love my wife, and want her to be happy, and I do genuinely enjoy political discussion and debate, to the extent that one can be had in any sort of real way with someone. So, it's no skin off my back to take the time sit there and break down the fallacies embedded in each of his arguments. There are also other family members being cc'd who are I think persuadable.