Why did president truman feel he had no choice but to drop the atomic bombs?
he feared that japan would mount a fresh attack on u. s. forces.
he felt that without the bomb, a costly invasion would be necessary.
he feared a japanese invasion of the california coast.
he believed he needed to defeat japan first before defeating germany.

He felt that without the bomb, a costly invasion would be necessary.  

Explanation:

Many historians believe that the launch of atomic bombs into Japanese territory was an inevitable decision in the face of Japan's refusal to surrender. Japan's permanence in the conflict left President Truman with few options, so he concluded that without the bomb, a costly invasion would be necessary . For this reason, he considered that the atomic bomb would be the best choice to establish an order and reduce the number of deaths an invasion would cause.

step-by-step explanation: