WASHINGTON (AP) — Nine months ago, President Joe Biden signed a sweeping bipartisan gun law, the most significant legislative response to gun violence in decades.

“Lives will be saved,” he said at the White House.

The law has already prevented some potentially dangerous people from owning guns. Yet since that signing last summer, the tally of mass shootings in the United States has only grown. Five dead at a nightclub in Colorado. Eleven killed at a dance hall in California. And just this past week, three 9-year-olds and three adults were shot and killed at an elementary school in Nashville, Tennessee.

A day after that school shooting, Biden’s tone was markedly less optimistic than it was the signing ceremony.

“What in God’s name are we doing?” he asked in a speech Tuesday, calling for a ban on so-called assault weapons like those that were used to kill at The Covenant School in Nashville. “There’s a moral price to pay for inaction.”

Biden and others had hailed last year's bipartisan gun bill — approved in the weeks after the shooting of 19 children and two adults at a school in Uvalde, Texas — as a new way forward.

Several months in, the law has had some success: Stepped-up FBI background checks have blocked gun sales for 119 buyers under the age of 21, prosecutions have increased for unlicensed gun sellers and new gun trafficking penalties have been charged in at least 30 cases around the country. Millions of new dollars have flowed into mental health services for children and schools.

But the persistence of mass shootings in the United States highlights the limits of congressional action. Because the law was a political compromise, it did not address many Democratic priorities for gun control, including universal background checks or the ban on “assault weapons” for which Biden repeatedly has called.

Now, in the wake of the Nashville shooting, Congress appears to have returned to a familiar impasse. One of the top Republican negotiators on the gun law, Texas Sen. John Cornyn, has said new compromise is unlikely. In the House, the new GOP majority favors fewer restrictions on guns, not more.

Asked Thursday about a way ahead, House Speaker Kevin McCarthy, R-Calif., said legislation alone cannot solve the gun violence problem. He said Americans need to think deeply about mental illness and other factors that drive people to act.

In contrast, House Democratic leader Hakeem Jeffries of New York said Congress should “act with the fierce urgency of now.”

“Our classrooms have become killing fields," he said. “Is that acceptable in America?”

Democratic Sen. Chris Murphy of Connecticut, the lead negotiator on the 2022 bill, says he thinks it represented a paradigm shift in how Congress considers gun legislation. But, he said, “I don’t think that will happen all at once.”

“This is sickening, but the opportunities for legislative change normally come after really terrible mass shootings,” said Murphy, who has been the lead Senate advocate for gun control since the 2012 mass shooting at an elementary school in Newtown, Conn. “I hate that, I wish that wasn’t how it works.”

Tensions were running high on both sides of the Capitol this past week.

On Wednesday, Rep. Jamaal Bowman, D-N.Y., stood outside the House chamber and yelled that Republicans are “cowards” for not doing more on gun control, eventually arguing with Rep. Thomas Massie, R-Ky., who advocated for allowing teachers to carry guns.

“More guns lead to more deaths!” Bowman screamed at Massie. “Children are dying!”

In the Senate, Republican Ted Cruz of Texas tried on Thursday to force a vote on legislation that would boost police presence at schools. He all but blamed Democrats, who had blocked the same legislation last year, for the Nashville shooting and calling the 2022 law “meaningless.” Murphy angrily objected to Cruz's bill, arguing that Cruz wasn't serious about compromise and that his move was a stunt for the cameras.

Despite the frustrations, lawmakers who negotiated the compromise last year say they see slivers of hope.

Murphy said the implementation of the new law, and some of its early successes, will ultimately persuade Republicans to get on board with more legislation.

“What happened last year was seismic for Republicans,” Murphy said.

In terms of the bill's success, “People don’t get excited about the mass shootings that didn’t happen,” Murphy said, and that can be a challenge as they talk about it and contemplate what more could be done. But the dynamics can change quickly, he said.

While Republicans in the past might have tried to shy away from gun measures even if they supported them, Cornyn and Sen. Thom Tillis, R-N.C., have been promoting the new law and discussing it frequently. Late last year, they joined Murphy, Sen. Joe Manchin, D-W.Va., and FBI Director Christopher Wray on a visit to an FBI facility in West Virginia for a briefing on how the background checks were working.

“I am proud to see this commonsense legislation already making a difference,” Tillis said in a statement afterward.

According to recent data obtained by The Associated Press, those who were flagged in the stepped-up background checks and prevented from buying a gun included an 18-year-old in Nebraska who had made terroristic threats and was prone to violent outbursts, a 20-year-old drug dealer in Arizona and an 18-year-old in Arizona who had been previously charged with unlawful possession of weapons and was found carrying fentanyl. All were attempting to purchase long guns.

Tillis said he is aware of a separate case in his home state where a person under 21 who had been charged with assault and battery and assaulting a police officer was flagged and prevented from buying a gun.

"It's just one of those bills that's going to age well," Tillis said, noting that the number of denials of gun sales is a very small fraction of total sales.

Cornyn said that so far, the bill “seems to be working.” But he said he doesn't expect Congress to go any further any time soon. He said would strongly oppose an “assault weapons” ban, as Biden is proposing.

When Biden and other lawmakers talk about “assault weapons,” they are using an inexact term to describe a group of high-powered guns or semi-automatic long rifles, such as an an AR-15, that can fire 30 rounds fast without reloading.

Most Republicans are steadfastly opposed to such a ban, arguing that it would be too complicated, especially as sales and varieties of the firearms have proliferated. There are many more types of these high-powered guns today than in 1994, when the ban was signed into law by President Bill Clinton.

Law- abiding citizens own those guns, Cornyn said, and “no law-abiding citizen is a threat to public safety.”

Despite the current standstill, John Feinblatt, president of Everytown for Gun Safety, a gun control advocacy group, says last year’s bill was proof that they can break gridlock.

“It was never the finish line,” he said.

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Associated Press writers Lisa Mascaro, Kevin Freking and Farnoush Amiri contributed to this report.