Question

What was a concern of some scientists after the Manhattan Project?
With Germany defeated, they did not think that Japan would be a threat.
They did not think that Truman was knowledgeable enough about atomic options.
With Germany defeated, they did not think there was a need for an atomic weapon.
They did not think the US had adequate staffing to continue development of weapons.

Answer 1

With Germany defeated, they did not think there was a need for an atomic weapon.

Many Manhattan Project scientists (e.g., Szilard and others) argued the bomb had been developed to deter Nazi Germany and, after V‑E Day, opposed using it on Japan without a demonstration or international discussion.