The Missouri Republican Party thinks linking guns to nullification works well, said Matt Wills, the party’s director of communications, thanks in part to the push by President Obama for tougher gun laws. “It’s probably one of the best states’ rights issues that the country’s got going right now,” he said.

The measure was vetoed last month by Gov. Jay Nixon, a Democrat, as unconstitutional. But when the legislature gathers again on Sept. 11, it will seek to override his veto, even though most experts say the courts will strike down the measure. Nearly every Republican and a dozen Democrats appear likely to vote for the override.

Richard G. Callahan, the United States attorney for the Eastern District of Missouri, is concerned. He cited a recent joint operation of federal, state and local law enforcement officials that led to 159 arrests and the seizing of 267 weapons, and noted that the measure “would have outlawed such operations, and would have made criminals out of the law enforcement officers.”

In a letter explaining his veto, Mr. Nixon said the federal government’s supremacy over the states’ “is as logically sound as it is legally well established.” He said that another provision of the measure, which makes it a crime to publish the name of any gun owner, violates the First Amendment and could make a crime out of local newspapers’ traditional publication of “photos of proud young Missourians who harvest their first turkey or deer.”

But the votes for the measure were overwhelming. In the House, all but one of the 109 Republicans voted for the bill, joined by 11 Democrats. In the Senate, all 24 Republicans supported it, along with 2 Democrats. Overriding the governor’s veto would require 23 votes in the Senate and 109 in the House, where at least one Democrat would have to come on board. 

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