Quote from AAAintheBeltway:
"Universal jurisdiction" is not accepted by the courts of this country. They would not extradict a defendant to face charges brought on such a basis. Of course, if the Germans were able to arrest Rumsfeld or other officials, then they could exert jurisdiction, much as was done with Pinochet when a craven British government detained the liberator of Chile. Most likely, there would be severe diplomatic repurcusions if Germany purported to try US officials. This type of insult is another good example of why the US should be vigilant to protect our sovereignty and reject supranational power grabs like the International Criminal Court.
It would be more for show if nothing else. Of course universal jurisdiction is not accepted by our courts. I don't even know how Germany has the gall to act as if they can carry out their judgments in this capacity anyways.