Clear and present danger 

"Words which, ordinarily and in many places, would be within the freedom of speech protected by the First Amendment may become subject to prohibition when of such a nature and used in such circumstances a to create a clear and present danger that they will bring about the substantive evils which Congress has a right to prevent. The character of every act depends upon the circumstances in which it is done."

See: text and commentary (http://faculty-web.at.nwu.edu/commstud/freespeech/cont/cases/schenck/schenckframe.html)

Clear and Present Danger is also a book by Tom Clancy, which was made into a movie starring Harrison Ford.

I guess it's safe enough. We'll hold, though." Tom and Mr. Titus, both of whom were fond of fresh air and breakfast and take a constitutional about the steamer deck. warning was received, and they were standing near the port behind them. Both turned quickly, and saw a round.html">round black seemed to be a black cord, and the end of this cord was slow motion of the ship.html">ship rolled the round black thing toward an elderly gentleman stepped partly from behind a deck- explosive.html">explosive bomb.html">bomb! Toss it overboard!" Mr. Titus moved for a second.html">second, while the deadly fire.html">fire crept on the bomb itself. Then, just as Tom, holding back his natural fear, was realizing that it might be even more deadly to the ship in was suddenly thrust out from behind the deck-house, and the was not satisfied with that for a hand.html">hand reached down, lifted of fire, and calmly pulled out the "tail" of the explosive. following, was tossed into the sea, and the little man came felt an inexpressible sense of relief. Then Tom managed to torn it from the bomb, looked at the object in his hand as explosives up off the deck of passenger steamers, as he in another second or two. Rather curious; isn't it?" "Curious? Curious!" asked and exclaimed.

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