It was a back down because the US wanted permanent immunity or else it would gather its toys and go home. The EU, Japan, etc. played some brinkmanship with this and succeeded in keeping the court alive and forcing the US to compromise. Chomksy and his acolytes, I suspect, see the ICC as an institution for providing cover for big powers should they want to prey on smaller/poorer countries via humanitarian interventions. The rabid conservatives in the US Congresssee it as an infringement on US sovereignty, so it has to be killed.
Peter