DENVER — Two days after the fourth anniversary of the Boulder King Soopers mass shooting, the Colorado House passed legislation to limit the sale of certain semiautomatic firearms to Coloradans who have passed a background check and taken a training course.

Senate Bill 3 — which would apply the new restrictions to the gun used in the Boulder attack — passed the House 36-28 on Monday. The bill’s Senate sponsors next will move to accept changes made in the House and then send the bill to Gov. Jared Polis.

The governor is expected to sign the measure. At Polis’ behest, lawmakers agreed to weaken the bill’s initial intent of fully banning the sale or purchase of the targeted weapons, unless they were altered to have a fixed magazine — meaning that they could not be reloaded as rapidly.

Still, the measure represents the strongest gun-control legislation passed by Colorado lawmakers since they began undertaking firearm regulation in earnest more than a decade ago.

The bill, which would take effect Aug. 1, 2026, broadly would prohibit the sale, purchase or transfer of gas-operated, semiautomatic firearms that accept detachable magazines — a definition that captures most firearms colloquially known as assault weapons.

Under the bill, the guns could still be purchased by people who’ve passed a background check and completed a training course. The legislation does not ban the possession of any weapon, and it would not apply to common pistols and shotguns. It also exempts a list of common guns, some of which are used for hunting.

The restrictions would apply to the gas-operated pistol used by the King Soopers shooter in March 2021. It would also cover the weapons used in the December 2021 Lakewood and Denver shooting spree; the 2012 Aurora movie theater shooting; and some of those used in the 1999 Columbine High School shooting.

The bill’s sponsors — Democratic Reps. Andy Boesenecker and Meg Froelich — said the bill regulates weapons with a “unique lethality” that have been used in mass shootings across Colorado and the United States.

“A generation after Columbine — (a time) of active shooter drills, of lived experience of mass shootings — you bet I have emotions,” Froelich, an Englewood legislator in her final term, said before the vote Monday. “I’m heartbroken. I’m also determined.”

'The core root of the issue'

Republicans uniformly opposed the bill in the House and the Senate. On Monday, House Republicans questioned the measure’s constitutionality and its usefulness, and they said the law wouldn’t be followed by the people most likely to commit violent crimes.

“Deal with violence,” said Rep. Anthony Hartsook, a Parker Republican. “… The tool that is used is an extension of that violence. Until you address the crimes and the people and the mental health that’s dealing with (violence), you’re not going to get to the core root of the issue.”

SB-3 is the product of months — and, in some ways, years — of debate, negotiation and broader political shifts, all against a backdrop of seemingly ceaseless mass shootings. After two years of failed attempts to pass assault weapons bans, lawmakers introduced the measure in early January with a different approach: banning the sale of many guns that accept detachable magazines.

It’s sponsored by Sen. Tom Sullivan, a Centennial Democrat whose son, Alex, died in the Aurora theater shooting. Sullivan had opposed the previous attempts at more explicit assault weapons bans, but he provided pivotal support for SB-3. He cast it as a way to ratchet up enforcement of the state’s high-capacity magazine ban — which lawmakers passed after the theater shooting.

When the bill was introduced, it had enough House and Senate co-sponsors to clear both chambers. But Polis sought a loophole, a desire enabled by a group of holdout Senate Democrats and the absence of a would-be supporter, then-Sen. Sonya Jaquez Lewis, for the vote.

After acceding to the training and background check changes, Sullivan and co-sponsor Sen. Julie Gonzales shepherded the bill out of the Senate. It was then heavily amended in the House, largely to cut costs in a tight budget year.

Once the Senate’s sponsors accept the House’s changes, the bill goes to Polis. Earlier this month, Polis said he was “confident the improvements made to the bill will … protect our Second Amendment rights here in Colorado and improve the education and gun-safety knowledge of gun owners.”

Significant new gun regulation

Should Polis sign it, SB-3 would be a cornerstone of Colorado’s growing foundation of gun control legislation, and its passage shows just how far the state has moved in the last decade.

In 2013, Democratic lawmakers passed a package of gun-control bills, including the magazine ban. That prompted a successful campaign to recall two Democratic legislators, which then chilled additional gun legislation.

That attitude has changed as voters have increasingly sent Democrats to the statehouse. Those Democrats have grown more comfortable pursuing firearm regulation in a state plagued by mass shootings.

In the past several years, the state has adopted age limits, waiting periods, storage requirements, state permitting for gun sales, and a red-flag law allowing for the temporary removal of a person’s firearms.

Still, SB-3 prompted extensive and heated debate in both chambers, including for several hours before the final vote Monday.

The state’s history of mass shootings was also omnipresent: In response to Republican criticism that the bill would limit “law-abiding citizens” from purchasing firearms, Denver Democratic Rep. Jennifer Bacon read the names of people killed in schools and grocery stores.

Each of them, she said, was a law-abiding citizen who “died of the crime of mass shooting.”

“I want us to recognize,” she said, “that we can prevent the crime of mass murder by gun.”

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