Greenwald on German prosecution of Rumsfeld

Greenwald comes out against prosecution of Rumsfeld et. al. in German courts:

But Germany continues to claim the power to subject other countries' citizens to its laws, to be convicted by its judges and sentenced by its government, even if those citizens have nothing whatsoever to do with Germany or with German citizens. That is nothing less than a claim to worldwide power -- to subject individuals to the rule of the German political system even though those individuals have no say in that system and no representation in it. In short, it is the assertion of government rule without even the presense of consent by the governed.

What possible justification is there for the German Government to assert legal power over other countries' citizens for acts that were not committed in Germany or to German citizens? And how can anyone justify having Americans subjected to trial by German courts and German judges under German law, when they have no representation whatsover in the German system of government?

I was happy about this development when I first heard about it (and reported it here), but I think Greenwald has a good point. I did argue that it should be the United States that prosecutes Rumsfeld and the other torturers (which I suspect include Bush, but let's get the evidence). I was arguing from a point of national honor, but legally it would be more sound, since there's no doubt about jurisdiction.

It seems to me that no matter what the Military Commissions Act says about who can be prosecuted, if Rumsfeld violated treaty law he can be prosecuted. According to the Constitution, treaty law supersedes all other kinds of law, so Congress can't just override it without actually amending the treaty. I assume that the Geneva Conventions are part of treaty law, no?