Against what threat did harry truman establish loyalty oaths during his presidency?

Loyalty oaths in the US were initiated during the 1950s and 1960s.  During the 1950s during Soviet annexation of eastern European Nations and developing a Nuclear Threat.

Senator Joseph McCarthy swayed the Nations thoughts to concern about communist spies, agents and saboteurs and a fear agents may injure the U.S. government through espionage or violence.

They were basically to secure the loyalty and well being of American citizens.

ok sorry the answer is a. by their religion