The Cold War reached a crisis point in June 1950 when Harry Truman announced that
the US would send troops to Korea to battle an invasion of the South by troops from
Communist North Korea. Two days after Truman launched the US into the Korean War,
the Caltech Board of Trustees moved in private to investigate "whether Dr. Pauling’s
services are detrimental to the Institute, and whether his appointment should be terminated."
Then a former Communist Party member and managing editor of the Daily Worker, Louis Budenz, provided the FBI the names of hundreds of people he claimed were concealed Communists.
One of them was Linus Pauling. The FBI kept the Budenz list secret while they tracked
the named suspects during the summer. The FBI investigation of Pauling uncovered no
evidence that he was a Party member -- many others on Budenz’s list were also found
not to be Communists -- but the professor’s actions were considered suspicious enough
that in October Pauling was given a place on the Security Index, the FBI’s list of
America’s highest-profile Communist sympathizers, "fellow travelers" as they were
called, all of whom Hoover considered a threat to America. Every one in the Index
would be constantly monitored and their files updated every six months.
At the same time, Joe McCarthy, the right-wing Senator, pulled Pauling’s name from
the Budenz testimony and publicly denounced him as a security risk who threatened
to give away America’s atomic secrets to the Russians. It did not matter much what
Pauling said in response. His name had been blackened; he was now inextricably linked
in the public mind to those trying to subvert US interests.