At least 19 people have been fatally shot in mass attacks since Saturday evening, when a 72-year-old gunman here opened fire inside a dance studio popular with the elderly Asian American community. Eleven people died in this city on the edge of Los Angeles, and then on Monday, two shootings in the Bay Area killed eight others.

State lawmakers have imposed mandatory waiting periods on the purchase of firearms. They have banned military-style assault rifles, one of only eights states along with D.C., to do so. The state has a “red flag” law that allows guns to be seized from people believed to be a threat. And California voters overwhelmingly approved a limit on the number of bullets allowed in a gun’s magazine, a measure caught up for years in the courts.

But the consensus among many lawmakers Tuesday was that there are simply too many firearms in the country and too many ways to get ahold of them without a national effort to pass stricter gun measures.

“What the hell is going on?” Gov. Gavin Newsom (D) said in angry remarks delivered after visiting with victims’ families in Half Moon Bay, a beach town south of San Francisco where a 66-year-old man is accused of killing seven farmworkers the previous day. “But it was said and said again: ‘Only in America.’ This happened on our watch. We allowed this to happen.”

Newsom said the state needs help from the federal government and a Republican Party that once supported some gun-control measures but has become deeply opposed.

“Where’s the Republican Party?” Newsom said. “One state can’t do it alone.”

There remained a host of questions Tuesday about the legality of the weapons used and whether state efforts, some now suspended by court challenges, should have kept the firearms out of the gunmen’s hands. Authorities have not provided specific details about how the gunmen in Monterey Park and Half Moon Bay obtained their weapons, among the hundreds of millions privately owned in the United States.

“We just have so many guns in circulation in this country that it is very difficult to prevent someone in crisis from getting access to one,” said Allison Anderman, senior counsel at the Giffords Law Center, a nonprofit organization that advocates for stricter gun laws. “We can do the best we can and make more laws at the state and federal levels — and still face enormous challenges in keeping guns out of the hands of people who shouldn’t have them.”

The shootings underscored again the grim reality that strict firearms laws cannot stop every shooting in a country where there are an estimated 400 million firearms, meaning that in the United States, guns outnumber people. The California state legislature takes up several gun-safety bills almost every year, and although some lawmakers said Tuesday that more of such measures must be passed, a specific agenda has yet to emerge after the recent shootings.

“Very determined people, even in a state with strong gun laws, can often find a way to get guns to commit acts of violence,” said Daniel Webster, a professor with the Johns Hopkins Center for Gun Violence Solutions.

But there was research, he said, showing that specific policies could reduce the frequency of mass shootings and other forms of gun violence.

“You don’t determine whether a state’s law is or isn’t effective based upon one or two or even three incidents,” Webster said. Instead, he said, it was important “to study this systematically over a long span of time.”

Even California’s gun restrictions, which are touted by Giffords as the strongest in the country, could still be strengthened in one key way, Webster said.

The state is “very quick to do a whole variety of things to try to regulate guns and minimize misuse of guns, far more than most states,” Webster said. “But they haven’t done what our research indicates seems to be the most effective measure at reducing all forms of gun violence … and that is to require a licensing process for people who purchase firearms.”

In 2020, Webster was the lead author on a study that found that licensing laws “really was the thing that correlated most strongly with reducing rates of fatal mass shootings,” he said.

California does have a registration process, but that’s different, Webster said. While some policies, such as banning large-capacity magazines, can be done with no real costs for law enforcement, that is not the case for establishing a licensing process, he said, given the personnel and work required. In states that have licensing processes, Webster said, the effort is borne by different agencies, including local departments in some places and state police elsewhere.

Still, even strict firearm laws have their limits — including the borders separating states.

“When there is a patchwork of laws and protections to various degrees across states, then clearly there are vulnerabilities,” Sen. Alex Padilla (D-Calif.) said during a Monday visit here.

In Chicago, police and city officials said in a 2017 report that most “crime guns” came from outside Illinois, a state with strict gun laws. The report found that 6 in 10 illegal guns recovered in Chicago came from outside the state; 1 in 5 illegal guns, the report said, came from nearby Indiana, a state with far more lax laws.

“Compared to other states, California has pretty tough gun laws,” said Jeffrey W. Swanson, a sociologist at the Duke University School of Medicine who has studied gun violence. But California is just one of 50 states, he said.

“The boundaries between states with different gun laws are open,” Swanson said. “You might have strict gun laws on the books in Chicago, but Indiana has different gun laws. And it’s very easy to get a gun in Indiana. ”

Swanson said the state gun laws that exist could be bolstered by more federal assistance.

“This is why … there’s some role for federal regulation,” he said. “And that’s where comprehensive, universal background checks are a good example. There are a lot of things you can do at the state level that would work better if you had background checks for every gun transfer.”

Questions still remained Tuesday about the guns used and recovered after the two recent mass killings in California. Republicans in the state legislature have little influence over gun-control measures given how outnumbered they are by Democrats, who hold a supermajority in both houses.

A Republican governor, George Deukmejian, signed California’s first assault-weapons ban in the late 1980s, months after a gunman killed five children at a school in the city of Stockton using such a weapon. But Republicans nationally have become far more resistant to gun-control efforts in the decades since, blocking most proposed federal legislation as an infringement on Second Amendment rights.

In Half Moon Bay, the attacker had a gun that was legally purchased, authorities said, but they did not elaborate on when and where it was bought.

Officials said that after the Monterey Park shooting, they recovered three guns linked to the shooter: a handgun found in the van where police say the gunman killed himself; a modified semiautomatic they said he used in the attack and then brought into a second dance studio, where someone disarmed him and took it; and a rifle found in his home afterward.

Los Angeles County Sheriff Robert Luna, whose department is leading the Monterey Park investigation, said at least one of the guns — the 9mm MAC-10 used to kill 11 people and wound another 10 — appeared to be banned. Luna said his comment was “based on the type of weapon it was.”

But authorities have so far not said when and where the guns were purchased. Luna said the attacker — identified as Huu Can Tran — had been arrested in 1990 for unlawfully possessing a firearm, though it was unclear whether that could have impacted his ability to obtain guns later on. Police have not said whether Tran was convicted of a crime in the incident — but if he had a felony on his record, it would have been illegal for him to possess a firearm.

Luna has said one key question is when Tran bought the weapons and whether that would have run afoul of the state’s evolving gun laws at the time. But he also said Tran had made modifications to the MAC-10 and had used a high-capacity magazine, which would violate state law prohibiting magazines that hold more than 10 rounds.

In addition to the rifle, police searching the gunman’s home found hundreds of rounds of ammunition and materials used to manufacture homemade firearm suppressors, Luna said.

The gun that the attacker was wielding when he went to a second dance studio appeared to be outfitted with a suppressor, said Adam Winkler, a professor at UCLA School of Law and an expert on the Second Amendment who reviewed a screenshot of security footage from that location.

“You couldn’t buy that in California and couldn’t lawfully modify your weapon in that way,” Winkler said.

Berman reported from Washington and Thebault from Los Angeles.