This came up
last year as well. Essentially, it's an attempt at reviving nullification, but the courts have routinely and unanimously rejected the doctrine for over a century.
We saw this a few years back with various states' "firearms freedom laws." Nobody stepped up to risk their skin to stir up a legal challenge. Considering that doing so could entail serious penalties on the federal level, I can't say I blame them.
There are two possibilities here. The first is that they're trying to create a test case on 10th Amendment grounds. If so, they're misguided.
The other is that they're simply pandering for votes from the true believers. If so, they're just being dishonest by selling a sense of false security. No way is a local Sheriff going to try and arrest ATF agents when they show up to do a bust.