Let's do reductio ad absurdum on this. Five people in the country may decide for any reason (threat, bribe, drugs, error) that it is constitutional to hang all Jews in the country. What then - sucks to be a Jew, or a redhead, or a lefty, or a gun owner, or anyone else who those appointed ministers of the King don't like?
The Article VI says this:
all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution;
It does not add "as interpreted by the current President, Congress or the Supreme Court." Perhaps there is a reason for that... Binding the Oath directly to the Constitition eliminates exactly these shenanigans, when various self-appointed interpreters of laws try to reinterpret them as it suits them today. The Constitution came from the people, and in the end it's the people's responsibility to support it.
Go read the paper I cited above. It provides a pretty clear history of failures to defend or enforce laws based on unconstitutionality by presidents.
As you can see from the table late in the paper, the failure to enforce a statute by the POTUS based on the thought that it was unconstitutional is hardly new or rare thing.
Here’s another paper on the topic:
http://georgetownlawjournal.org/files/pdf/96-5/Prakash.PDF..
The sheriff is on firmer legal ground than most people think. Especially since the sitting AG of the US has made this very argument himself.