From The New York Times:

Some sheriffs, like Sheriff Cooke, are refusing to enforce the laws, saying that they are too vague and violate Second Amendment rights. Many more say that enforcement will be “a very low priority,” as several sheriffs put it. All but seven of the 62 elected sheriffs in Colorado signed on in May to a federal lawsuit challenging the constitutionality of the statutes.

The resistance of sheriffs in Colorado is playing out in other states, raising questions about whether tougher rules passed since Newtown will have a muted effect in parts of the American heartland, where gun ownership is common and grass-roots opposition to tighter restrictions is high.