The US has the authorization of NATO, the UN and has acted in concordance with the mandates that these organisations have put up.  The US does not harm the powers of the US constitution by helping the UN and NATO in this area because the US committed to these organisations with the knowledge that it might have to compromise sometimes in order to fulfil the responsibilities it has taken on within these organisations.  Libya is simply an example of one of these compromises and this does not harm the constitution any further than the US initially did by entering into these agreements and institutions. 1, 2  Editorial: “Obama’s illegal war” The Washington Times. 18/03/2011  Stone, Daniel. “Is the Libya War Legal” The Daily Beast. 22/03/2011