A recent New York Times article wrote this about the US state of Maryland.
Zachary Clopton, a law professor at Cornell University, said Monday’s lawsuit may be more serious than the New York complaint because Maryland is legally considered a “coequal sovereign” with the president. That makes it a stronger opponent in the constitutional argument over emoluments, he said.
What does "coequal sovereign" mean in this context? And does it apply specifically to Maryland or to every state?
The only time I've heard of the idea of "co-equal sovereign" is within the doctrine of Dual Federalism. As suggested by this textbook it refers to
A system in which the states and the national government each remain supreme within their own spheres. The doctrine looks on nation and state as co-equal sovereign powers. Neither the state government nor the national government should interfere in the other's sphere.
However I don't believe this practically true any-more, as the Wikipedia article suggests:
The general consensus among scholars is that dual federalism ended during Franklin Roosevelt’s presidency in 1937
In fact most historical cases (at least in the last 100 years) have recognised the supremacy of the federal government over individual states, and I cannot find any other legal reference to whether Maryland (or any other state) any longer enjoys co-equal sovereignty.
The wider point the professor is trying to make, about a State filing a case against the President being more serious than other non-government actors filing such a case is however valid.
