Answer:
A. The central part of the U.S. Constitution to both the Brandenburg v. Ohio (1969) and the earlier case of Schenck v. United States (1919) is the First Amendment. The First Amendment guarantees freedom of speech, religion, and the press, as well as the right to peaceably assemble and petition the government.
B. The Supreme Court ruled in favor of Brandenburg but against Schenck because of the different interpretations of the First Amendment's protection of freedom of speech. In Schenck, the Court held that speech that posed a "clear and present danger" to the nation's security could be regulated, while in Brandenburg, the Court established the "imminent lawless action" test, which only allows speech that incites imminent violence to be regulated. The Court in Brandenburg found that the Ohio law was too broad in scope, as it did not make a distinction between speech that incited violence and speech that only called for violence in general.
C. The Brandenburg case can be seen as a reinterpretation of the First Amendment since the time of the Schenck case. The Court's decision in Brandenburg represents a more protective stance on freedom of speech, as it requires a higher level of evidence to prove that speech is a threat to public order and safety. The "imminent lawless action" test used in Brandenburg provides a more nuanced approach to free speech compared to the "clear and present danger" test used in Schenck. The Brandenburg case is seen as a more narrow interpretation of the First Amendment, which has since been used as a precedent for the protection of free speech in the United States.