The group, which announced a $50 million campaign last year to support gun-control candidates and legislation, spent more than $110,000 in Oregon last year, with a focus on shifting a few important legislative seats that would lead to majority support for the background check law that Ms. Brown signed.

It went into effect in August.

Even with the new law, the main contours of who can and cannot buy a gun in Oregon mirror those of most other states in the nation, where the Supreme Court has ruled that the Second Amendment protects individuals’ right to bear arms. No license is required simply to purchase a handgun or a long gun, though when going to their local gun shops to buy firearms people must pass background checks conducted by the State Police that bar people who have felony convictions, have been involuntarily committed to a mental health institution, or fall into certain other prohibited categories.

When it comes to a license to carry a concealed handgun, Oregon is what is considered a “shall issue” state, which means that for the most part, local authorities have little discretion to deny someone such a permit.

Sheriffs do have the right under the law to deny someone a permit if there are “reasonable grounds” to believe the person is a danger to himself or others as a result of his mental state or “past pattern of behavior involving unlawful violence or threats of unlawful violence.”

The gunman in Roseburg, identified as Christopher Harper-Mercer, 26, did not appear to have warranted a denial. Federal officials said all 13 of his guns, including six found at the scene, were legally obtained by him and his relatives.