No, states are NOT obligated to enforce federal law.

[Lee-Lee]

8. Not only are they not obligated- they don't have authority to enforce a Federal law

When I was a deputy I came across many violations of Federal law.

All I could do was refer the case to the relevant Federal authority. I as an officer sworn by a state/local authority could not charge anyone with a violation of Federal law.

One example- I had an ongoing domestic case I was working. The couple was separated, and there was a restraining order against the husband. Because of that he was ineligible to buy to posses a firearm. He talked the woman he was seeing to do a straw purchase and buy him a shotgun.

I was able to charge him because NC has a law that parallels Federal law saying that he couldn't posses a gun. Straw purchase laws are Federal, so I couldn't charge her. I sent it to the BATFE, who didn't do anything.

It's also why Congress can't set speed limits. Those are state laws enforced by state officers. Instead the only think Congress can do is more or less blackmail the states by saying if they don't make their laws in what they want they will withhold funding related to it. But only Congress can do that in a budget bill, it can't be a unilateral move by the executive.