He authorized its development by the US.
FDR
He didn't. All he had to do with the atomic bomb was signing a letter written by Leo Szilard that was sent to FDR.
FDR never saw a working atomic bomb, he died before the first ones were built.
To convince FDR to support building an atomic bomb before Germany did so.
FDR ordered its development.Truman ordered its use.
It is thought that he would have nixed the actual usage.
An atomic bomb is a nuclear bomb.It can kill lots and lots of people
FDR
He signed a letter that Leo Szilard wrote to FDR. That is all.
Not at all.
Not really.
None, Einstein had no part in either inventing or making atomic bombs except to sign a letter to FDR that Leo Szilard had written. Leo Szilard is the inventor of both the atomic bomb and reactor.