1. Where the United States expressly reserves jurisdiction over a federal enclave, but permits a state to exercise concurrent jurisdiction, does such grant of concurrent jurisdiction divest the federal courts of the jurisdiction that they would otherwise have under the Enclave Clause?

2. Alternatively, does federal question jurisdiction require that a "'right or immunity created by the Constitution or laws of the United States must be an element, and an essential one, of the plaintiff's cause of action,'" or is it sufficient that the case implicates substantial federal issues?

Whether the grant of concurrent jurisdiction divests federal courts of enclave jurisdiction