>>718306945
That's the entire point. Saruman was corrupted so badly by his skype chats with Sauron that he was playing mental gymnastics against his own best interests. Saruman genuinely believed that if he pretended to help Sauron by actually helping Sauron, he could then outwit Sauron by backstabbing him later once he gets his hands on the One Ring to give him an edge. Saruman was no longer rational, he was putty in Sauron's hand. Same goes for Denethor, albeit Denethor at least never accepted the idea of cooperating with Sauron, no matter what.
