You say the Buddha was in exile towards the end of his life?
In Rajgir, the king now was not Bimbisara, but Ajatasattu, who had not only overthrown his father, but had plotted with his teacher Devadatta to overthrow the Buddha. It appears that in Vaishali too he had lost his support. During the last rain retreat in Vaishali, he doesn't stay in his usual place, which is a house with gabled roof in the great forest, but he stays in a little village outside the city walls by himself and he tells his monks to go and find lodging in the city for their support. Now this is strange--why does he do that? One possible reason for this is because he had recently been denounced to the Vaishali parliament by a man called Sunagatha, who was formerly a monk in the Buddhist community who then disrobed, left the community and went to the Vaishali parliament and said, "The monk Siddhartha Gautama is a fake." So we know that he's probably lost favour in Vaishali, he's lost favour in Shravasti, his homeland is under attack, the Magadhans were treating him just as a sounding board for their next war. What you see in fact is that the Buddha falling out of favour essentially corresponds to the loss of his main benefactors. During the last nine or 10 months of his life, he's constantly on the move, which again suggests this fact of exile.
You also conclude that the Buddha may have been deliberately poisoned?
He had no shortage of enemies. Pava, where he had his last meal, was one of the two principal towns of Malla, the Kosalan province adjoining Sakiya. Karayana, the general of the Kosalan army now laying waste to Sakiya, came from Malla, possibly from Pava itself. Pava was also where Mahavira, the ascetic founder of Jainism is said to have died a few years earlier, and when the Buddha arrived there was already a shrine to his principal rival. The text only says that the Buddha is invited to a meal along with his attendant monks at the house of a man called Cunda the smith. Cunda prepared a meal of sukaramadhava, tenderised pork, something like ham or bacon. From the moment it was offered to him, it seems that the Buddha suspected something was amiss with the food. "Serve the pork to me," he told his host, "and the remaining food to the other monks." When the meal was over, he said to Cunda:" You should now bury any leftover pork in a pit." Then he "was attacked by a severe sickness with bloody diarrhoea, which he endured mindfully without any complaint." His only response was to say to Ananda: "Let us go to Kusinara", which under the circumstances, sounds like "Let's get out of this place."