Nick, I am not a US lawyer, so you will have to direct your inquiries elsewhere. I only checked the language of the law because I knew that Iran was ordered to pay damages to a victim of Hamas (for supporting that organization) and it seemed odd that the case against Dichter will be thrown out of court. Now we know the reason. I have no idea if the constitutionality of the exemption was tested before the US Supreme Court. The Court does not initiate cases, only adjudicates them. If you are interested in such a test, I would suggest that you recommend to the present plaintiffs or lawyer to appeal the District Court's decision. My suspicion is that the law will be found constitutional since the principle of foreign government's immunity makes sense in general. The exception can be questioned, not the rule.
One dead, three injured in Northern Arizona University shooting (DPA)
from the article: U.S. District Court in Manhattan clears Dichter in war crimes suit