Why did the committee advising President Truman recommend that bomb should not be demonstrated and instead should be used against the enemy

Explanation:

At the time the U.S. dropped the atomic bombs on Japan, there were only two bombs produced. There was a worry therefore that sparing one bomb simply for a demonstration would be a waste.

There was also no guarantee that the demonstration would work because the Japanese had shown themselves particularly stubborn in the struggle. A situation might have arrived therefore where the Americans would demonstrate the bomb and the Japanese would keep fighting which would have meant that the bomb was wasted.