a) Being a christian really only requires a declaration of belief, AFAIK b) I’m genuinely convinced a lot of grifters believe their own bs. Not all of it, obviously, but I think he really does believe that he is a christian paragon and that the US should be returned to being christian nation, and any falsehood he knowingly advances is justified because it advances those goals. Not to say that this wouldn’t change if the tides in US politics turned, but I’m pretty sure that most professional liars like him genuinely eat their own manure.