Can one legally write a book on how to Assasinate the President?

How far does the clause “For educational use only” hold up legally. Could one actually write a book on How to assasinate the President, How to build a bomb, or How to hack your cable modem to steal service and claim it is for “educational use only.” Does free speech protect this? if so to what extent?

I think there was a supreme court case on this but I can not remember what it is.