Secession in the North

Apparently the Secretary of State for Ohio has approved for inclusion on the fall ballot a proposed amendment to the Ohio Constitution which would bar enforcement of federal health insurance laws.  The Secretary thinks the proposal has enough signatures to get to the ballot.  Okay.  But the proposal is unconstitutional -- state laws, even state constitutions, cannot supersede federal law.  Not in some contested sense or on the margin.  The Supremacy Clause of the US Constitution says so.  I don't grasp how patently unconstitutional provisions get approved -- is it just that the Secretary has a purely ministerial role of counting signatures?  Why would one not be able to enjoin inclusion on the ballot of a proposal which, even if passed, cannot be law?  It is puzzling.  Isn't this just an effort at state nullification?  How could a lawyer defend it?  Will have to look a bit further.