How did this happen, he asks himself, even as all of Saruman's planning and scheming replays itself behind his eyes. It seems an odd question, but he is far beyond rationality; the lands around Orthanc tremble with the shouts and snarls of the Uruk-Hai, and his fear rings in his ears, sets his teeth on edge. Somehow he never believed it would happen this way. He thought it would serve them all right. An entire land subjugated, a court deceived—by an advisor to the king! The thought amused him. Theoden would pay for his arrogance. And his pretty niece, the one with fancies of glory in battle, she was like a glorious mare, cold and passionate...defiant. If he could break her with his words, make such a proud woman bow before him, do his bidding...and with Saruman's help, his sly tongue could easily corrupt such an innocent mind.
A little taste of humiliation for those proud, witless horselords who sat on their crowns and made their sport drinking themselves into a fog and reciting the allegedly glorious accomplishments of their ancestors as an insult to those they judged to be of inferior heritage. Fools all. What guidance could be found in ancestry? He was not immune to the greatness of Eorl—but what right had his sons to claim his glory for themselves? Theoden's people called themselves Eorlingas, but they donned stolen laurels; they had done nothing to merit the honor of such a name. He would not make such an ass of himself. He would be greater than any of his idiot fathers who had drooled at the king's right hand and begged that his discretion might land on their suggestion. And so betrayal was so simple. What allegiance did he owe Rohan? Theoden would bow and scrape to earn his honor!
He was overcome with glee at his assigned task: to use his great powers of wordplay to turn Theoden Horsemaster into a dotard! Nothing could be closer to his purpose. Eomer had little power at court; he was only a lieutenant, subject to the whim of those who laid stratagems for battle. He was insignificant. With Theoden gibbering uselessly on the throne and Eomer easily outwitted and disposed of, nothing could stand between him and his prize! And with Rohan's lady in his possession, the throne would soon follow. Heads would roll, and blood would pour, or so Saruman said. But it was not to be his blood, and what did it signify if some hapless Rohirrim fell on their own spears when Rohan became his for the taking?
And then the Stormcrow challenged his hold over the dotard king. It was a cruel blow; the wizard had outmaneuvered him. And the fool king, released from his prison of woven words, nearly chopped his head off. To be rescued by a Dunedan, an exile who had nothing to recommend him but a skill for eluding hungry beasts in the wild! He raced to rejoin Saruman; such humiliation would be short-lived. They would all pay. The wizard and the Dunedan would suffer especially; he would see to it. He would chain them by their necks to the walls of Orthanc and let the birds feast on their flesh.
And now he stands on the battlements of the tower, gazing out on the imminent destruction of the land and folk he has always known to be his. Such a proud race, his people, who should have been his to rule, but for the interfering Lathspell—to suffer so, to be wiped from the face of Middle Earth, only for the misfortune of calling a simpleton and a braggart their lord and king! He stands with wide eyes fixed on a vision of peasants and horsemasters huddled inside the dank walls of Helm's Deep, the men preparing for battle and death, the women minding the children and scrounging for food, and he weeps. One tear, as payment for bloodshed and betrayal. Not the betrayal of weakening their leadership, of handing their fate to Saruman and his ten thousand monsters. Under Theoden's banner, he knows, Rohan must fall. He weeps for the betrayal of waiting calmly for the sunrise.