President Obama has refused to enforce parts of the law merely because he dislikes them, so it's hard for leftists to complain if sheriffs refuse to enforce gun restrictions on Constitutional grounds. I think it's legit for every American citizen who happens to hold a government position to personally ensure that their official behavior is in line with the Constitution.
Side note: just as we are wary of the federal government strangling the sovereignty of the states, we should push for state governments that respect the liberty of counties and municipalities.
When Sheriff John Cooke of Weld County explains in speeches why he is not enforcing the state's new gun laws, he holds up two 30-round magazines. One, he says, he had before July 1, when the law banning the possession, sale or transfer of the large-capacity magazines went into effect. The other, he "maybe" obtained afterward.
He shuffles the magazines, which look identical, and then challenges the audience to tell the difference.
"How is a deputy or an officer supposed to know which is which?" he asks.
Colorado's package of gun laws, enacted this year after mass shootings in Aurora, Colo., and Newtown, Conn., has been hailed as a victory by advocates of gun control. But if Sheriff Cooke and a majority of the other county sheriffs in Colorado offer any indication, the new laws -- which mandate background checks for private gun transfers and outlaw magazines over 15 rounds -- may prove nearly irrelevant across much of the state's rural regions.