Major Texas Republican donors took out a full-page ad in the Dallas Morning News on Sunday, calling on lawmakers to pass gun control regulations, including so-called red flag laws, less than two weeks after the deadly mass shooting at an elementary school in Uvalde, Texas.

Over 250 self-declared "gun enthusiasts" -- including contributors to Republican Gov. Greg Abbott's election campaigns -- signed an open letter supporting bipartisan gun reform legislation.

Red flag laws, officially known as extreme risk protection orders, allow law enforcement to seize firearms from those deemed a risk to themselves or others. Such measures have already been passed in 19 states, including Republican strongholds like Indiana and Florida. 

While GOP leadership has traditionally been against gun regulation, the deadly mass shootings in Uvalde, Buffalo and Tulsa since mid-May have led to rare bipartisan support in Congress and statehouses across the US. On Saturday, a brawl on Philadelphia's South Street turned deadly as at least two men opened fire, killing three people and injuring 12 more.

In a June 2 address, President Joe Biden called for federal 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."

Here's what you need to know about red flag laws, including how they work, where they exist and whether such legislation could be passed by Congress

What are red flag laws?

Red flag laws allow extreme risk protection orders, or ERPOs, to be issued to temporarily stop high-risk individuals from keeping, buying or selling guns, according to the Seattle Police Department, "when there is demonstrated evidence that the person poses a significant danger" to themselves or others.

While specifics vary from state to state, the orders also often prevent a person from obtaining a concealed weapon license and require them to surrender their permit if they have one.

Factors that can trigger an order include violent behavior or self-harm, substance abuse and a "dangerous mental health crisis," according to Seattle police.

Where have red flag laws been enacted?

To date, 19 states and the District of Columbia have mechanisms to issue extreme risk protection orders on the books: California, Colorado, Connecticut, Delaware, Florida, Hawaii, Illinois, Indiana, Maryland, Massachusetts, Nevada, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont, Virginia and Washington.

Maine's "yellow flag" law is unique in that it requires approval from both a judge and a medical care provider before firearms can be seized.

More than half of all red flag laws were passed after the deadly 2018 attack on Parkland, Florida's Marjory Stoneman Douglas High School, where a former student used a semi-automatic rifle to kill 17 people and injure 17 others.

In May 2020, Oklahoma became the first state to pass legislation specifically prohibiting any jurisdiction from enacting red flag laws.

Who can request an extreme risk protection order?

Most red flag laws only allow family members, household members or police to petition the court to seize someone's firearms, but a few let school officials, medical professionals and even employers and co-workers make the request.  

Are red flag laws successful?

Because red flag laws are a recent gun control measure -- and mass shootings are still relatively rare compared to other forms of gun violence -- solid data is hard to come by. According to Everytown for Gun Safety, though, red flag laws "are a proven way to intervene before an incident of gun violence."

"Extreme Risk laws give key community members a way to intervene before these warning signs escalate into tragedies without going through the criminal court system," the gun regulation nonprofit said in a statement on its website.

At least 16,857 ERPOs were filed between 1999 and 2021, 90% after the 2018 Parkland shooting.

According to Everytown, in California, gun violence restraining orders (the state's version of an ERPO) have averted several mass shootings -- including an incident where an employee at a car dealership threatened to shoot his supervisor and other employees if he was fired.

After his manager informed law enforcement and a GVRO was obtained, five firearms were seized.

Everytown also reports that temporarily removing guns from people in crisis significantly reduces the risk of firearm suicide, which results in the deaths of at least 24,000 Americans each year. 

Most guns used in mass shootings are purchased legally -- in stores, at gun shows and online -- making tracking and intervention with ERPOs easier. And the deadliest mass shootings are carried out by young men under 25, who may still be living at home with family members who can petition for an order.

Still, some state law enforcement officials have expressedreluctance to enforce the orders. Colorado Sheriff Steve Reams told CNN in 2019 that he'd rather go to jail than enforce a red flag law.

And even if police do enforce an order, a judge will only issue one for a specific timeframe. 

Could Congress pass a red flag law?

While no federal red flag law has cleared both chambers on Congress, leaders in both parties have signaled support for such a measure. In August 2019, after back-to-back shootings in Dayton, Ohio, and El Paso, Texas, that killed 31 people, then-President Donald Trump said laws should be passed to ensure individuals "judged a grave risk to public safety do not have access to firearms."

That same year, Republican Sen. Lyndsey Graham of South Carolina and Democratic Sen. Richard Blumenthal of Connecticut indicated they were working on a measure to provide funds to states that pass red flag laws.

The bill was never introduced, however. 

On June 2, House Democrats held a special session of the Judiciary Committee to mark up the Protecting Our Kids Act, a package of measures intended to stem gun violence. And Democratic Sen. Chris Murphy of Connecticut told The Wall Street Journal he was discussing a red flag bill with Senate Republicans, including Sens. John Cornyn of Texas and Susan Collins of Maine.

Whether those talks lead to substantive legislation, though, is questionable.

"Several different times we've had conversations among members and at markups about the desirability and the relevance" of red flag laws, Sen. Chris Coons, a Democrat from Delaware, told Axios. "That should be enactable, but in the several years since, despite repeated efforts ... we haven't been able to get to 10 on that."

What is the opposition to red flag laws?

House Minority Whip Steve Scalise, a Republican from Louisiana, called the measures "unconstitutional." 

"They literally come into your house and take away your gun without you even knowing that there was some kind of proceeding where somebody said, 'Oh, I think that gun might be a threat,'" Scalise told Fox News' John Roberts. "Maybe somebody thought taking away a gun from a 19-year-old is going to solve a problem. It happens to be unconstitutional."

The National Rifle Association has also expressed concerns about red flag laws, saying they could interfere with an individual's right to due process.