This sheriff is making the same decision (about different laws) that the President makes every day when he directs the Attorney General to avoid prosecuting violations of laws passed by Congress and signed into law by his predecessors.
Exactly. In Obama’s case, it was the DOMA law.
And no less a legal authority than Eric Holder has made this argument.
Here’s a nice little paper on the subject:
http://www.columbialawreview.org/wp-content/uploads/2012/07/112-3_Devins_Prakash.pdf
NB the table late in the paper of various statutes a list of presidents have failed to defend in court on Constitutional grounds.