Is Harry Truman a war criminal?

I infer the question is related to the decision to use nuclear bombs on Japan in Hiroshima and Nagasaki.
On August 6, 1945, the United States Military dropped an atomic bomb on the Japanese city of Hiroshima. Approximately 85,000 people died, and many were Japanese civilians. Many more would suffer death from the effects of radiation in the first few weeks of the aftermath of the explosion. Countless others would die an early death, as generations suffered from the destruction and impact of radiation still active in the soil and water of Japan. Many years later, scientists would discover the radioactive dust from the blast would enter into the atmosphere and be deposited on other continents. The second blast, which took place on August 9, 1945, on Nagasaki killed an estimated 40,000 additional Japanese citizens, and many suffered from the aftermath, just as they did from the first bomb dropped on Hiroshima. The second blast resulted in the surrender of the Japanese and may have been the most controversial. The use of the atomic bomb shook up the international order and created an arms race as other countries quickly concluded they needed a weapon of equal power as a defensive and offensive military advantage.
Truman did not decide to use the atomic bomb lightly. It was clear that World War II was winding down. Ally troops had regained control of the war-torn European front, and all that remained to be defeated was an intransigent Japan refusing surrender or to acknowledge it was time to seek peace. After learning of the successful test of the atom bomb in July, Truman was reported to have called it "the most terrible bomb in the history of the world." Truman was fully apprised of the potential immediate destruction, as his scientists and military observers had witnessed the destructive power of the weapon. But what other options did Truman have to end the war?
Truman could have continued bombing Japan with conventional weapons. The war would be prolonged, and there was no guarantee that prolonged bombing would result in fewer civilian casualties over time. It was certain that American soldiers would continue to suffer losses from the Japanese military continuing the fight indefinitely. The increased bombing had not been useful as a tactic, as the Japanese grew more hostile and resistant to surrender when more bombs were deployed against them. Some preferred a massive invasion of Japan by American and European forces, much like the Normandy invasion. Europeans had little interest to continue a war, particularly one that was far from their continental shores. An invasion would impede Europe rebuilding the cities devastated by war. The invasion was the least viable of the options.
The third option presented to Truman was to drop the bomb on a deserted island near Japan, demonstrating the power and destructive capability that would be rained upon the Japanese if they did not surrender. Military advisers were not in favor of losing the element of surprise and they did not want to risk an international backlash, so this option was nixed.
The remaining option was to choose targets that contained large military complexes to avoid civilian casualties. Hiroshima and Nagasaki were selected from a list. Civilian casualties would be minimized to the extent the horrors of war can be surgically separated from military and civilians. Given the options, Truman was conflicted as to what to do, although the final solution appeared to be the best of the worst: drop the bomb to end the war.
The first bomb was dropped, and the power unleashed upon military and civilian alike. Truman did not shy away from taking responsibility for the death and destruction caused by the first bomb. Within a few short days, the second bomb was dropped, effectively ending the war. Should Truman have given the Japanese more time to respond to calls to end the war before dropping the second bomb? This is the question that brings into the debate if Truman should be prosecuted for war crimes: was the second bomb necessary?
Some historians believe the Japanese were on the verge of surrender from the result of the pounding they were taking from American bombers. If this was the case, then the question is of whether Truman violated international law that defines war crimes as when superfluous injury or unnecessary suffering is inflicted upon an enemy or humanity? This is the debate that has dogged historians since the end of the Second World War.
Your answer to the question is entirely dependent on your point of view. If history is a guide, then generally only leaders who perpetrate the most serious of heinous activities (e.g., Hitler or genocide more broadly) explicitly directed at civilian populations that violate international standards for war crimes are prosecuted by international courts as war criminals. Truman intended the bomb be directed at military populations and intentionally selected targets where the least amount of civilian casualties would occur.
The history of warfare would support the conclusion Truman was not a war criminal. If you advance the proposition that the dropping of the first bomb may have been the only option to end the war and that dropping the bomb saved lives in the long run by forcing Japan to surrender, then the second bomb was unnecessary. There is some evidence to suggest Japan was ready to quit, but they were seeking a negotiated term to save themselves from the humiliation of defeat. Then you may well answer the dropping of the second bomb meets the criteria of superfluous injury or unnecessary suffering having been inflicted upon an enemy. The issue of criminality cannot be dismissed without evidence to the contrary. The physical evidence of correspondence and transcribed notes from meetings with military leaders suggest Truman intended to bring a quick end to war and civilians were not intentionally targeted. Yet, good intentions may not be enough to excuse bad outcomes.
The question is not quickly answered. What can be said since the day of the second bomb being dropped is that although weapons of war have become more sophisticated, accurate, and increasingly more destructive, nuclear bombs have not been used since. That alone does not speak to the question of criminality, but it certainly speaks to the question of the morality of using nuclear devices in battle.
https://www.atomicheritage.org/key-documents/truman-statement-hiroshima

https://www.history.com/topics/world-war-ii/bombing-of-hiroshima-and-nagasaki

https://www.nps.gov/articles/trumanatomicbomb.htm