August 6 is the 67th anniversary of the bombing of Hiroshima, the first and, thankfully, next to last time nuclear weapons have been used as a weapon of war. The usual analysis is that President Harry Truman decided to use atomic bombs because he wanted to avoid large scale U.S. casualties in the event of an American invasion of the Japanese home islands and alternative uses, such as a demonstration explosion, were not likely to force the Japanese to surrender.
I think a case can be made that Truman ordered the attacks because he didn't want to waste money and that he was president because Missouri wasn't getting enough pre-war defense contracts.
Here's the logic chain: Truman got to be President because he was FDR's Vice President. FDR selected him as running mate because he was a popular lawmaker with fewer political problems than the other likely candidates, Henry Wallace and James Byrne. He was well known and well regarded because of his leadership of a committee investigating wartime contracting. He got that job because he had proposed creation of such a committee and the competing chairmen of the military and naval affairs committees didn't want the other to chair, so Truman was a compromise. He proposed creation of the committee because some businessmen from Missouri complained that they weren't getting their fair share of rearmament contracts.
Given his background of exposing government waste, it's inconceivable that Truman would forego using a weapon developed in secret for almost $2 billion -- over $21 billion in today's dollars.
I don't see sunk cost as the necessary or sufficient condition for the use of the A-bombs, but it must have been a factor.