It seems to me that this wouldn’t be much different from state attempts to nullify federal gun laws.
Basically, this would be a state nullifying federal espionage laws (or whatever the feds are attempting to charge him with). The state would likely have to explicitly say “We will arrest any federal official who attempts to enforce these laws in our state” which is essentially what some have said with gun laws.
Then, in the end, it comes down to whether or not the feds are willing to call the state’s bluff and risk a violent confrontation, or not.