The first amendment to the constitution states that congress or the president may limit free speech when it is in "the best national interest" to do so.

The wording in the First Amendment ensures that freedom of speech is not absolute. As all liberties and freedoms, the limit is the public good and national interest. This does not mean government can arbitrarily suspend freedom of speech, and in fact the First amendment prevents any censorship based on simple suspicion. To act against freedom of speech, there must be enough reasons an evidence to justify it: someone selling national secrets, or publishing sensible information, or producing hate speech that might lead to riots are cases to consider, but the suspension of the First Amendment, even in this cases is complicated.