The Manhattan project did leak info to the Soviets. It is true it stayed out of public view for several years, but a difference in the Manhattan project is that

The Manhattan project did leak info to the Soviets. It is true it stayed out of public view for several years, but a difference in the Manhattan project is that every single person involved was investigated by the FBI beforehand, and the country was so heavily united in the fight against the Axis powers that it is quite likely almost everyone involved was a true believer.