[FerniesApple]

I have a theory that Sauron never contemplated that the Ring was in the hands of the Hobbits until he 'saw' Pippin in Minas Tirith through the Palantir Denethor was using. He may have come to know that a Hobbit was living in Minas Tirith by forcing Denethor to give up information against his will, probing his mind or thoughts. I think Sauron thought the attack would come from Minas Tirith rather than through the backdoor, he allowed Denethor to use the Palantir, not because a mortal had the resilience to resist but to gain information and spread disinformation like propaganda. No mortal could resist a direct atack from Sauron, only Aragorn had the mental strength and that not for long on his own.