It only takes one willing governor. If the state Nullifies the law, usually this is done through legislation -- but a zealous governor can easily perform this on his own -- then the state will simply refuse to enforce the law.
If the state chooses to interpose the law, through similar methods, it chooses to actually "interpose" their state law enforcement in between the "criminals" and the federal law enforcement; the state chooses to prevent the federal police from enforcing the law.
These ideas are enshrined in the 10th amendment (a now dead amendment that everyone has forgotten about -- but one that has yet to be repealed), and were first laid out by Thomas Jefferson and James Madison in the "Kentucky and Virginia Resolutions of 1798".
If you'd like to learn more, which I DEMAND you do, check out the book "Nullification" by Thomas E. Woods Jr. You can easily find links to it through my hubs - I loved the book and recommend it on just about all my newer hubs.