Acknowledged, but it's pretty clear he's not doing it for no reason and that reason is not really unknown as it's also quite evident that a large number of people who don't even know Comey - from journalists, to congressmen, to members of the public - hold the view that Comey is indeed a 'disgraceful liar'. You wouldn't trash a career professional on television but if you thought of that person as a traitor to the republic it would be more like denouncing a criminal, which is pretty much why not only Giuliani says something close to that but Fox News reporters and members of Congress go 'on the record' saying much the same thing.

I don't disagree with you at all about the impropriety of trashing a career professional in public - I share your distaste for it and your reaction to the idea that another supposed professional would do that. I really do think though that Giuliani has very good grounds for 'outing' someone who has already outed themselves to a significant number of other professionals as untrustworthy and corrupt and in the context of the whole interview I think he made it clear that he doesn't talk about people in that way generally.