Why isn't anything being done about Blackwater? Why won't the media cover this?

Not being a lawyer, I might be mistaken about this, but isn’t Blackwater’s involvement with US wars a violation of the Constitution?

As I understand it, the President is the Commander-in-Chief, and thus directs the armed forces, but he needs approval from Congress to declare war. The US armed forces are answerable to the US government, and consequently, the American people. Blackwater, as a hired agency, is answerable to the president alone. Is the president allowed to have a personal fighting force? How is this different from the SS, Hitler’s personal army, separate from the armed forces of Nazi Germany?

This seems like a pretty big deal to me, but I don’t see this being discussed in the media. In fact, Bill Maher is the only one I’ve seen discussing it, and pretty much only when Jeremy Scahill is a guest.