The gist of the book's thesis (at least so far as I understand from as much as I've read) is conveyed pretty well in this article in which Wills attempts to explain why President Obama has been so quick to adopt the imperial powers the Bush administration had itself excersised.
A president is greatly pressured to keep all the empire’s secrets. He feels he must avoid embarrassing the hordes of agents, military personnel, and diplomatic instruments whose loyalty he must command. Keeping up morale in this vast, shady enterprise is something impressed on him by all manner of commitments. He becomes the prisoner of his own power. As President Truman could not not use the bomb, a modern president cannot not use the huge powers at his disposal. It has all been given him as the legacy of Bomb Power, the thing that makes him not only Commander in Chief but Leader of the Free World. He is a self-entangling giant.In the book, after noting the finding of the Summary Report of the United States Strategic Bombing Survey of 1946 that:
It seems clear that, even without the atomic bombing attacks, air supremacy over Japan could have exerted sufficient pressure to bring about unconditional surrender and obviate the need for invasion. Based on a detailed investigation of all the facts, and supported by the testimony of the surviving Japanese leaders involved, it is the Survey's opinion that certainly prior to 31 December 1945, and in all probability prior to 1 November 1945, Japan would have surrendered even if the atomic bombs had not been dropped, even if Russia had not entered the war, and even if no invasion had been planned or contemplated.Wills goes on to observe
Whether an invasion of Japan occurred or not, the mere possibility of its happening without use of the Bomb was a nightmare prospect to Groves and other officials. If it became known that the United States had a knockout weapon it did not use, the families of any Americans killed after the development of the Bomb would be furious. The public, the press, and Congress would turn on the President and his advisers. There would have been a cry to impeach President Truman and court-martial General Groves. The administration would be convicted of spending billions of dollars and draining massive amounts of brainpower and manpower from other war projects, and all for nothing. This was the truly terrifying prospect that made use of the Bomb an easy, if not inevitable, choice for those who had harbored their secret project so long and wanted to reveal it with a supreme vindication. Groves even suggested that Truman would be betraying the memory of President Roosevelt, who authorized the Bomb's development, if he rejected its use. The Bomb's tenders had put themselves in a position where they could not not use it. They were now the prisoners of their own creation.Reading this - and from previously having heard Wills discuss the book in various venues - I can't help but think of the narrator in the George Orwell essay "Shooting an Elephant."
Afterwards, of course, there were endless discussions about the shooting of the elephant. The owner was furious, but he was only an Indian and could do nothing. Besides, legally I had done the right thing, for a mad elephant has to be killed, like a mad dog, if its owner fails to control it. Among the Europeans opinion was divided. The older men said I was right, the younger men said it was a damn shame to shoot an elephant for killing a coolie, because an elephant was worth more than any damn Coringhee coolie. And afterwards I was very glad that the coolie had been killed; it put me legally in the right and it gave me a sufficient pretext for shooting the elephant. I often wondered whether any of the others grasped that I had done it solely to avoid looking a fool.Of course, in Orwell's essay, the self-oppression of colonialism results in the narrator killing an elephant. In the case of the atomic bomb, it resulted in the killing of hundreds of thousands of civilians.
For more on the book, see Wills at Fora.tv