The argument for "red flag" laws is built on researchers and government agencies' finding that most mass shootings are preventable if citizens, health professionals and courts can act on signs of troubling behavior in time.

Why it matters: Although mass shootings only account for a fraction of firearm deaths in the U.S., advocates are pushing for a preventative approach to keeping guns out of the hands of people believed at greatest risk of committing violence. Red flag laws may also be a rare point of bipartisan consensus as the nation grapples with a surge of mass shootings.

State of play: Red flag laws are built around what's known as extreme risk protection orders that allow certain citizens or law enforcement to petition a court to remove gun access from a person believed capable of committing homicide or suicide.

• The laws currently exist in 19 states and the District of Columbia. Bipartisan gun reform talks in the Senate include a measure that would incentivize more states to enact such laws, and President Biden called for a national red flag law in a speech last week.
• "We should also have national red flag laws so that a parent, a teacher, a counselor can flag for a court that a child, a student, a patient is exhibiting violent tendencies, threatening classmates or experiencing suicidal thoughts," Biden said.

The big picture: Data backs up anecdotal evidence from one mass shooting after another that there are almost always observable signs of the violence to come, and experts say there are consistent patterns of behavior.

• "Even though there's considerable variability between the individuals, what they’re doing is largely the same," said Jaclyn Schildkraut, interim executive director at the Regional Gun Violence Research Consortium at the Rockefeller Institute of Government, who recently wrote a blog post describing the path to violence.

Zoom in: A U.S. Secret Service analysis of 41 school violence incidents that occurred between 2008 and 2017 found that "all attackers exhibited concerning behaviors. Most elicited concern from others, and most communicated their intent to attack."

• A 2019 study examining the 15 deadliest public mass shootings in the U.S. between 1998 and 2018 found that "most incidents were indeed preventable based on information known about offenders in advance, and that the deadliest mass shooters exhibited more warning signs and were more often reported to law enforcement than other active shooters."
• An FBI study of the pre-attack behaviors of 63 active shooters found that each displayed an average of four or five troubling behaviors that were observable to others.

Between the lines: Red flag laws are straightforward in theory and directed at preventing people exhibiting concerning behaviors from possessing guns. But it all comes down to how the laws are applied.

• "It's one thing to pass a law and it's another to bring it to life," said Shannon Frattaroli, a professor at Johns Hopkins Bloomberg School of Public Health whose research includes red flag laws. "Right now, we really are at a place where implementation is crucial."
• In some states with such laws on the books, "we have hundreds of those petitions in which someone came forward to the court and said we are here to request an ERPA because this person has communicated verbally, has communicated online, is amassing weapons, is fill in the blank ... and we’re concerned," Frattaroli said. "If this is used more, there’s potential for great aversion of deaths to occur."

The other side: Gun rights groups argue that red flag laws violate a person's right to due process as well as their Second Amendment rights.

By the numbers: Since Florida's red flag law was passed after the Parkland school massacre in 2018, judges have acted more than 8,000 times to temporarily prohibit an individual from buying or possessing a gun, CNN recently reported.

• However, a Wall Street Journal analysis published last year found that many jurisdictions have used the laws rarely or not at all.
• A study of the use of Washington state's red flag law in King County found that of the 75 petitions filed, only five where the threat was to other people met a definition of a mass shooting threat. Respondents were described as being at risk only to themselves in 40% of petitions, to only others in 27%, and to both in 33%.
• Another study found that Connecticut and Indiana's firearm seizure laws resulted in meaningful reductions in firearm suicides.

Details: Who can file petitions under the state laws also varies. 13 states and D.C. allow family or household members to submit a petition in addition to law enforcement, but a handful of states only allow law enforcement to be petitioners, according to the Giffords Law Center.

• Maryland and D.C. allow mental health providers to petition, New York allows school administrators to do so, and Hawaii allows medical professionals, coworkers, and educators.

The bottom line: "This is a new approach that we're using in gun violence prevention. For all of our history, we've been reactionary," Frattaroli said.

• "You see very consistently the types of behaviors and the patterns and the expressions of harm that I think most reasonable people would agree, gosh, there's something going on with this person right now, and it's just not a good idea for them to have access to a gun."