Under Federal Law, the overt act is not a necessary element.
United States v. Shabani, 513 U.S. 10 (1994), was a decision by the Supreme Court of the United States regarding conspiracy liability under federal statutes. The Court ruled: "...Congress intended to adopt the common law definition of conspiracy, which does not make the doing of any act other than the act of conspiring a condition of liability..." This ruling indicated that conspiracy alone can be criminal.
Well in that case they have no excuse to raid and shut down every Islamic training camp in the country.
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