The Espionage Act demonstrated that at one time the federal government was willing to limit fundamental rights, such as the right of freedom of speech, in order to prevent any action that weakened the US during warfare times.
The Espionage Act was a federal law enacted in 1917, after the US started its intervention in WWI. It aimed to prevent any interferences with military activities and recruitment (the draft), to prevent any insubordination in the armed forces, or the support of US enemies either directly, or through any action which could weaken the US.
The decision adopted by the US Supreme Court in Schenck v. United States, evidenced that even the fundamental civil rights guaranteed by the First Amendment to the US Constitution, more specifically, the right of freedom of speech, could be limited in situations that harmed the strenght of the US during wartime.