Ever since the 2012 massacre at the Sandy Hook School in Newtown, Conn., gun-control advocates have worked hard to close so-called "loopholes" in background-check laws.

Not all the efforts have been successful; gun-rights advocates say such measures are needlessly burdensome and do little to stop violent crime. But last year, Washington state residents voted to toughen the state's background-check laws. And now the Oregon legislature has done the same.

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