President Joe Biden mourned the killing of at least 19 children and two teachers in a mass shooting at a Texas elementary school, decrying their deaths as senseless and demanding action to try to curb the violence.

"I hoped, when I became president, I would not have to do this again," Biden said at the White House, in sometimes halting, emotional remarks. "Another massacre in Uvalde, Texas. An elementary school. Beautiful, innocent, second, third and fourth graders."

"As a nation," he said, "we have to ask: When are we going to stand up to the gun lobby? When are we going to do what we know in our gut needs to be done?"

Tuesday's massacre at Robb Elementary School is the latest in a string of mass shootings that have rocked the country. Just 10 days ago, a gunman in Buffalo, New York, opened fire at a supermarket, killing 10 people in a racist attack.

The attack in Uvalde, which is about 80 miles west of San Antonio, is the deadliest U.S. school shooting since a gunman killed 26 people, most of them first graders, at the Sandy Hook elementary school in Newtown, Connecticut, in 2012.

The shooter, an 18-year-old, was killed Tuesday by responding officers. Texas State Senator Roland Gutierrez, a Democrat from the region, said in an MSNBC interview that the man had bought his weapons legally on his 18th birthday.

Across the U.S., anger overflowed among Americans who have long demanded, to no avail, that federal lawmakers do anything to prevent gunmen from perpetrating horrific violence, especially against children. After the Sandy Hook slayings, President Barack Obama and Senate Democrats sought to pass new gun-control measures only to see the legislation blocked by Republicans, who have suffered no electoral consequences for their opposition to even modest restrictions on civilian weaponry.

Connecticut Democrat Chris Murphy, who was elected to the Senate a month before the Sandy Hook shooting, delivered an angry, impassioned speech on the Senate floor imploring Congress to pass gun-control legislation.

"Our kids are living in fear every time they set foot in a classroom because they fear they will be next. What are we doing? Why do you spend all this time running for the United States Senate?" he asked. "Why do you go through all the hassle of getting this job and putting yourself in a position of authority if your answer, as the slaughter increases and our kids run for their lives, is we do nothing?"

Biden was briefed on the Uvalde shooting aboard Air Force One as he returned to Washington from a trip to South Korea and Japan. He ordered U.S. flags to be flown at half-staff through May 28 and also called Texas Governor Greg Abbott to offer federal assistance.

Reflecting on his trip to the two Asian democracies, Biden said, "What struck me was these kinds of mass shootings rarely happen anywhere else in the world."

"Why? Why are we willing to live with this carnage?" he asked.

The president, who lost one of his children in a car accident and another to cancer, expressed condolences to Uvalde parents who, he said, "will never see their child again, never have them jump in bed and cuddle with them."

The anniversary of the death of Biden's son Beau, who was 46 when he succumbed to brain cancer in 2015, is on Monday.

With gun-control legislation stalled on Capitol Hill, the president has little to offer but yet another call to action and grief for the victims' families. Biden didn't call for specific measures but said that when the U.S. had an assault-weapons ban in place, from 1994 to 2004, mass shootings declined, and then "tripled" after the law expired.

"Don't tell me we can't have an impact on this carnage," Biden said.

Democrats have repeatedly tried and failed to enact new gun-control measures, including universal background checks and an assault-weapons ban, in the decade since Sandy Hook. Multiple proposals have been blocked by Republicans and a handful of centrist Democrats.

Republicans have close ties to the gun lobby. Former President Donald Trump and other leading Republicans, including Texas Senator Ted Cruz, are scheduled to speak at the National Rifle Association's annual meeting this weekend in Texas. Guns are not allowed in the venue.

David Hogg, a gun-control activist who survived a 2018 school shooting in Parkland, Florida, told CNN early Wednesday that he believed action was possible.

"I do believe that this time can be different. Americans are tired of debating this issue. The time for debate is over. The time for action was yesterday," he said. "A reduction — stopping one more school shooting, one more act of violence — is worth it."

"We have to focus on what we can agree on. If you are Republican, work with us! We need to do something to save these children," he said.

But on Tuesday, Republican Senator Jim Inhofe of Oklahoma said he could conceive of no legislation that would prevent attacks like Uvalde.

"It would be very difficult," he said. "You're talking about millions of people out there, and there have got to be some screwballs that are just totally unpredictable. And there's no way to identify who they are. So none that I can think of."

Legislation expanding gun background checks to sales at gun shows and online cleared the Democrat-led House in March of last year on a 227-203 vote and a second bill cleared, 219-210. That bill would prevent gun sales from proceeding if a background check isn't completed within three days as allowed under current law.

But in the 50-50 Senate, where at least 10 Republican votes are needed to muscle past a filibuster, both measures stalled.

Senate Democratic Leader Chuck Schumer moved late Tuesday to put two gun background-check bills on the Senate calendar, teeing up potential floor votes.

Jenny Leonard, Laura Litvan and Alexis Shanes report for Bloomberg News.

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