that TheodenTheoden would turn from Gandalf to go back to Saruman. At the time I was still thinking much of Theodred, and I couldn't see TheodenTheoden forgetting his son easily : it was one thing not to want to go to war openly, to let himself be convinced by GrimaGrimaGrima, not to want to inflict the same suffering to his people, and quite another being an overt ally of Saruman. I don't think that before Gandalf's arrival at Edoras he had properly realised he was in fact acting at Saruman's bidding. He felt himself weak and let himself be influenced by GrimaGrimaGrima, a long-time counselor, he took what seemed the easy way, but I don't think that once his eyes had been opened by Gandalf he was susceptible to fall again in Saruman's trap.
For me his reluctance to speak and his heavy speech were rather indications of his sad memories.

As  for his men, some of them seem to have been fooled by Saruman's voice and besides, for people with no knowledge of politics, any offer of peace is not to be rejected lightly.

Wormtongue was duped by Saruman; as they have probably met one on one, Saruman's voice had all its power, his reasoning, however warped, was not contradicted, and he probably promised rewards (Eowyn ?). But as he listens to Saruman now, GrimaGrimaGrima too must at last realise the true nature of Saruman...

In a way, Gandalf's plan works perfectly : Saruman is losing control and his temper, such revealing to all (part of) his real personality. But at the same time the other part of his errant (saving Saruman) seems on a bad way...