Interpole and the US Constitution

Here is a report from Threats Watch on the Obama administration's decision to grant diplomatic immunity to Interpole. They argue that this is unconstitutional since, if they are operating under the rules of diplomatic immunity they are acting as a police force not bound by the provisions of our Constitution. They outline why this is likely to be a precursor to the US joining the ICC. It sounds pretty bad, but I will wait till I hear from some more mainstream legal scholars before I get too upset about it.