Good question, but I don't think so. State laws and the rights of the states supersedes federal law - under the 10th Amendment.
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
However, one could argue that the 2A is delegated by the Constitution -- so -- perhaps a case eventually for the SCOTUS?
The real issue isn't as much the Second Amendment itself. That was held in in
McDonald v. City of Chicago to be incorporated into the 14th Amendment's Due Process clause, and therefore applicable to states as well as the federal government. So, the 2nd Amendment applies to state governments despite the 10th Amendment.
The real issue is more procedural, and relates to the interaction between the police power and the courts. If Virginia's new law is unconstitutional, then it must be declared as such by federal courts, which would then strike it down. At that point, Virginia would not be permitted to enforce its law. But the courts are the mechanism to resolve that -- Trump really can't give a direct order to the state government, or order in federal troops, etc., absent a court decision/order.
What he can do is use the bully pulpit to try to convince Northam that this is a terrible idea.
