Can the States and County Sheriffs nullify federal law?

They are going to try.

Let's just look at today's news.

In Iowa, the Cedar County Sheriff says he won't enforce any new federal gun laws.

In Wyoming, the House of Representatives for the state gave approval to exempting guns in the state from any restrictions the feds might pass.

And an Arizona Senate panel passed a bill barring enforcement of federal gun measures.

We haven't had a good discussion of the concept of nullification, a state ignoring federal law, since the War Between the States in the 1860's.

Looks like one might be starting up.