Which gun control policies and could prevent mass shootings, according to a gun violence expert

Extensive universal background checks

While universal background checks have been at the forefront in the gun control debate, Wintemute said that there are several incremental holes in the implementing the policy that could still allow potential mass shooters to obtain a weapon, according to a VPRP study.

One of the holes includes that state and local law enforcement, as well as mental health authorities, are not required by federal law to report prohibiting events that would prevent an individual from gaining access to a firearm. Therefore, the prohibitions would not appear even if a background check were conducted.

The loophole led to mass shootings like in Southern Springs, Texas, where 26 people died at a church; Charleston, South Carolina, where nine people died in another church; and Virginia Tech, where 32 people died on the college campus, Wintemute said.

"Those mass shootings occurred after prohibited people cleared background checks and acquired firearms from licensed retailers, because their prohibitions were not in the data that the background checks were run up," he said.

Extreme risk protection orders ("red flag laws")

"Red flag" laws, also known as extreme risk protection orders, mandate intervention to be taken on a case-by-case basis "where the risk of violence to others or to oneself is judged to be extraordinarily high," Wintemute said.

"More than 80% of people who commit a mass shooting, in some way, declare their intent in advance," Wintemute said. "Their family or their friends or their social media network are aware that something is going on. And that's where extremists protection orders have had their role."

"This is see something, say something," he said.

Trump has expressed his support for extreme risk protection orders in the past, similarly his daughter and senior advisor, Ivanka Trump, also called for an increase in "resources dedicated to mental health support."

Along that thread, Wintemute noted that most people working in the field of violence prevention refer to the laws by their more formal title of extreme risk protection orders, as "red flag" laws are non-specific and stigmatize members of the mental health community.

"The thing that concerns me the most, frankly, is that the metaphor, "red flag law," inspires fear," Wintemute said. "But we're not trying to make people afraid, we're trying to empower them, because for this to work, participation of individual members of the public is absolutely vital."

"It's focused on behavior," Wintemute said. "It's not focused on mental illness."

Reinstating the ban on assault weapons and high-capacity magazines

Some 2020 Democratic presidential hopefuls have proposed the idea of reinstating the 1994 assault weapons ban, which sunsetted in 2004 during the Bush administration, as a solution to the recent spate of mass shootings.

"What the ban probably did was, for 10 years, delay the increase in prevalence of ownership of assault-type firearms, and we've seen that increase since 2004," Wintemute said. "To my knowledge, nobody thinks it's a coincidence that the increase in mass shootings in part relates to how common these weapons are."

However, he said that, while the AWB had been successful in the past, the same success is not necessarily guaranteed for its reinstatement.

"I think we can certainly make the argument that it might be beneficial to prevent [assault weapons] from becoming more common, but I suspect there are now millions of these weapons in circulation, millions of these magazines in circulation," he said.

Wintemute said that high-capacity magazines are the true culprit, as some rifles that don't typically fit the physical appearance of an assault weapon, thus not relating to the ban, can still accept the magazine.

"So if it's not a ban on possession, if we're not going to recover these firearms from civilian owners, the effects of a ban now would be blunted by the fact that there's so many of them out there," he said.

Restrictions on high-risk groups

"I think as we move forward with a broader effort to prevent firearm violence, we need to think about whether we should extend restrictions on purchasing and possessing firearms to some high-risk groups that are not now covered," Wintemute said.

One high-risk group that is not covered, Wintemute said, are people convicted of violent crimes. He said that "it's simply a myth that violent criminals cannot legally purchase firearms" on a federal level unless they are convicted of a felony.

He also noted that people who have been associated with alcohol abuse, such as driving under the influence, are four to five times as likely to commit violent crimes in the future compared to those who have no criminal record, a VPRP study showed.

"There is a wealth of data, associating alcohol abuse with risk of future violence, including future violence that involves firearms," Wintemute said.

Closing the boyfriend/girlfriend loophole

Minnesota Senator and 2020 presidential candidate Amy Klobuchar made it a priority to close the gap in gun legislation called the "boyfriend loophole," in which partners convicted of domestic violence can purchase a firearm if their partner was not a spouse, didn't have children with them, or live with them at any point.

"Under federal law, the definition of intimate partner does not include a boyfriend or girlfriend with whom one is not living, unless the couple has had children together," Wintemute said. "So a dating relationship, if you will, even though more than half of the intimate partner violence is at the hands of perpetrators who are in dating relationships with victim."

He went on to say that he thinks closing the "boyfriend" loophole could be a "straightforward fix," but it simply needs more awareness as an issue first.