The issue of gun control re-entered the national conversation following the shooting late Wednesday night at the Borderline Bar & Grill in Thousand Oaks. The attack left 13 people dead including the suspected gunman.

One question that is sure to be part of the debate in coming days: Could a proposition passed by California voters in 2016 — but since held up by legal challenges over its constitutionality — have prevented the suspected gunman from obtaining the ammunition he is alleged to have used?

California has worked to pass laws curbing the use of assault weapons and large-capacity magazines in the wake of the terror attack in San Bernardino in December 2015 in which 14 were killed.

In the aftermath of the attack, California voters passed Proposition 63 in November 2016 by an overwhelming margin. The measure, championed by then-Lt. Gov. Gavin Newsom, prohibited the purchase of magazines containing more than 10 bullets and mandated background checks before the purchase of large amounts of ammunition.

California has some of the most comprehensive gun control laws in the nation.

Prospective gun owners must file for a state permit to obtain firearms. There are laws limiting the purchase of assault weapons and .50 caliber BMG rifles. And most importantly for this case, there is a 2011 restriction on large-capacity magazines, a phrase the Legislature almost deliberately left vague.

Authorities have identified the shooter as Ian David Long. They said that the weapon he used was a Glock 21 .45-caliber handgun fitted with an extended magazine. Witnesses reported that he reloaded his weapon at least once, but Ventura County Sheriff Geoff Dean confirmed that the suspect had at least one large-capacity magazine. The required magazine and ammunition that were used could have been more challenging to acquire had Proposition 63 been enacted.

At least one legal expert agrees: Proposition 63 may have helped prevent this shooting.

Robert Spitzer, professor and chair of the Political Science Department at the State University of New York, College at Cortland, has written multiple books on the Second Amendment and gun control. He defends the constitutionality of Proposition 63.

"Case law would hold that it is constitutional to place the limit on 10-bullet magazine," he said in a telephone interview. "The notion that this is out of step with other legislation is untrue."

Proposition 63 attempted to amend the ambiguity of the earlier magazine restrictions — and it would have, had it not been challenged in federal court by a lawsuit filed by the California Rifle & Pistol Association (CRPA), a state chapter of the National Rifle Association. The May 2017 lawsuit claimed that the proposition was unconstitutional and labeled it a violation of Second Amendment rights.

On June 29 of that year, a federal judge ordered California Attorney General Xavier Becerra to withhold enforcement of the proposition until a decision on the lawsuit is made.

Thursday afternoon CRPA Executive Director Rick Travis issued the following statement:

"For once we agree with Governor-Elect Newsom: addressing societal problems has to be a priority in preventing tragedies like this rather than blaming millions of law-abiding California gun owners. In an era where 22 veterans a day on average commit suicide, it's shameful that more isn't being done."

Constitutional scholar Spitzer, in response to the CRPA statement, asked, "Are they suggesting that there are millions of law-abiding gun owners who own 30-round magazines?"

Could Proposition 63 have made it more difficult for Long to have obtained the ammunition he is suspected to have used — or even stopped him completely?

"The general answer would seem to be yes, depending on where or how he obtained the magazine that he did. That would be the purpose of the law after all," said Spitzer.

The suspected gunman had a history of domestic disturbances, according to NPR. He was the subject of a battery in 2015 and had been evaluated by a mental-health specialist due to his irrational behavior in the aftermath of the battery. A basic background check, mandated by Proposition 63, would have brought up this history of mental health and violence, ending his attempts to purchase the magazine and ammunition.