Blackwater.
Now there's an idea. From Article I, Section 8:
[Congress shall have the power to] declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;
From the Wikipedia article on Letter of Marque:
The issue of Marque and Reprisal was raised before Congress after the September 11, 2001 attacks[3], and again on July 21, 2007 by congressman Ron Paul. The attacks were defined as acts of "air piracy," and the Marque and Reprisal Act of 2001 was introduced, which would have granted the president the authority to use Letters of Marque and Reprisal against the specific terrorists, instead of warring against a foreign state. The terrorists were compared to pirates in that they are difficult to fight by traditional military means.[4] Congressman Paul also advocated the use of letters of marque to address the issue of Somali pirates operating in the Gulf of Aden on April 15, 2009.The issue of Marque and Reprisal was raised before Congress after the September 11, 2001 attacks[3], and again on July 21, 2007 by congressman Ron Paul. The attacks were defined as acts of "air piracy," and the Marque and Reprisal Act of 2001 was introduced, which would have granted the president the authority to use Letters of Marque and Reprisal against the specific terrorists, instead of warring against a foreign state. The terrorists were compared to pirates in that they are difficult to fight by traditional military means.[4] Congressman Paul also advocated the use of letters of marque to address the issue of Somali pirates operating in the Gulf of Aden on April 15, 2009.