The oath that is the basis for this movie's plot has several real precedents from U.S. history. In March 1947, President Harry S. Truman signed United States Executive Order 9835, which required U.S. government employees to swear that they were not members of any organizations that were deemed "subversive" and it authorized widespread investigations to search for "incriminating" details in government employees' pasts, including homosexuality. More commonly known as the "Truman Loyalty Order," it was largely driven by paranoia about the possibility of Soviet and other communist infiltration in government and other American institutions and is now seen as an early incident in the period known as the Red Scare. Another famous American loyalty oath was the Levering Act of 1950, a California state law that required every state employee to sign a statement attesting that they were not communists or members of any group that advocated the overthrow of the U.S. government. The University of California Board of Regents fired 31 professors (despite their tenured status) who refused to sign the oath on grounds of academic freedom and freedom of speech. The dismissals were eventually reversed by the California Supreme Court, but only after several years and lawsuits. As of 2018, several U.S. states still require their employees to sign loyalty oaths.