> When a state declares itself a Sanctuary State for, say, immigrants in the country illegally, what the state is actually doing is interfering with federal enforcement of federal laws, commonly referred to as obstruction.
Incorrect. And there's actually a very recent court decision that concurs with what I'm about to say.
No state (government) actively interferes with Federal law enforcement. Sanctuary cities/states take the position that they're under no obligation to render aid to ICE et al in enforcing Federal immigration law. A Federal court backed this opinion (again) in State of California et al v US Department of Transportation (25-cv-208-JJM-PAS).
Which ironically, you proved my point in your own post:
> it isn't the state's law to enforce
The states are saying this, and the Trump admin is trying to punish them for it - which is unconstitutional. I will also point out that the Constitution limits Federal power - the 10th Amendment says that powers not expressly enumerated are reserved to the States. I always find it amusing how all of these "strict constitutionalists" are suddently not when certain states do things they don't agree with.