Many state governments don't like high-handed federal laws like Obamacare and gun control. So, they nullify that law by declaring it unconstitutional. Some make enforcement a felony.
By contrast the US AG claims the US Constitution and laws pursuant thereto are supreme, the constitution and laws of the states notwithstanding.
We should consider the AG completely right... so long as the "laws" actually pursue the Constitution. If they don't, then they thereby become nullities and no one has to obey them.
"President" Obama himself proved the profound truth of the that theory by nullifying the natural born citizen clause in the Constitution. He did that by ascending to the Presidency in spite of not having natural born citizen status (if he is even a US citizen at all). The courts have trounced every effort to hold him accountable. So he should have no quarrel with the states that use the same principle to nullify laws they don't like.
Bottom line, every entity associated with government (including the electorate) has the right and duty to interpret the Constitution as it sees fit. And damn-to-hell (even in a clash of arms) anyone who disagrees.
If it's good for the goose (Obama), it's good for the gander (the States).