There are reports that the Obama administration may invoke the Responsibility to Protect as a legal justification for intervening in Syria. But like the other legal rationale being discussed, this one falls short for the basic fact that R2p can justify a military intervention only if the Security Council says so.
The Responsibility to Protect is the principle that governments have a duty to protect their citizens from genocide and crimes against humanity, and if governments fail in this duty the international community has the responsibility to intervene. “R2P” was codified at the 2005 UN Summit in a document that was signed by nearly every head of state. Here’s what the document says:
138. Each individual State has the responsibility to protect its populations from genocide, war crimes, ethnic cleansing and crimes against humanity. This responsibility entails the prevention of such crimes, including their incitement, through appropriate and necessary means. We accept that responsibility and will act in accordance with it. The international community should, as appropriate, encourage and help States to exercise this responsibility and support the United Nations in establishing an early warning capability.
139. The international community, through the United Nations, also has the responsibility to use appropriate diplomatic, humanitarian and other peaceful means, in accordance with Chapters VI and VIII of the Charter, to help protect populations from genocide, war crimes, ethnic cleansing and crimes against humanity. In this context, we are prepared to take collective action, in a timely and decisive manner, through the Security Council, in accordance with the Charter, including Chapter VII, on a case-by-case basis and in cooperation with relevant regional organizations as appropriate, should peaceful means be inadequate and national authorities manifestly fail to protect their populations from genocide, war crimes, ethnic cleansing and crimes against humanity. We stress the need for the General Assembly to continue consideration of the responsibility to protect populations from genocide, war crimes, ethnic cleansing and crimes against humanity and its implications, bearing in mind the principles of the Charter and international law. We also intend to commit ourselves, as necessary and appropriate, to helping States build capacity to protect their populations from genocide, war crimes, ethnic cleansing and crimes against humanity and to assisting those which are under stress before crises and conflicts break out.
140. We fully support the mission of the Special Adviser of the Secretary-General on the Prevention of Genocide.
R2p does not necessarily mean military intervention, but when military intervention is required the document very clearly states that the Security Council must authorize the intervention. That happened in Libya. But it would be spurious to invoke some parts of R2P to justify an intervention, while ignoring the parts of R2P that places limits on military intervention.