Question

what did Albert Einstein do when his letter had no effect​

Answer 1

Einstein was shocked after the bombing of Hiroshima and Nagasaki. As his letter had no effect , he got involved in world politics. He is reckoned as world citizen.

Answer 2

Albert Einstein came to the reality that his letters had no effect sooner or later. This made him enter the politics of the world.

Explanation :

Einstein along with other scientists was concerned about the weapons made and have warned the US government of potential threats especially German as Hitler became their newfound leader.

His letter to Franklin D Roosevelt resulted in the Manhattan Project but he was against the idea of nuclear fission as the strategy for their bombs.