While many Americans and politicians offered up thoughts and prayers off the news that 18 children and three teachers were killed in a Texas elementary school shooting on Tuesday, plenty of people also shared their frustration that gun violence has continued to plague the country for decades — and with little action from Congress. 

Gun-control advocates were among the most vocal on Twitter following the shooting at Robb Elementary School in Uvalde, Texas, which is the deadliest shooting at an American elementary school since the 2012 Sandy Hook massacre in Newtown, Conn.

Moms Demand Action, a grassroots organization advocating against gun violence that was founded after the Sandy Hook shooting, tweeted that “schools should be sanctuaries of safety for our children, not where they go to die.” 

And the organization’s founder, Shannon Watts, posted that school shootings are not acts of nature, but “man-made acts of inaction, of cowardice, of corruption by all lawmakers who refuse to pass laws proven by data to stop preventable, senseless shootings like in Ulvade.”

Gun-control advocacy group Everytown for Gun Safety tweeted: “If constant fear of gun violence isn’t a crisis, what is?” 

Former Arizona Congresswoman Gabrielle Giffords, who was severely injured in a mass shooting in Tucson, Ariz., in 2011, tweeted she was “devastated” by the Texas elementary school shooting, and called this “a uniquely American problem.” 

“How many more children will be killed by guns? How many young lives cut short, families shattered, communities traumatized because our leaders refuse to act?” 

Indeed, Connecticut Sen. Chris Murphy, a lawmaker from Sandy Hook’s district, went viral on Tuesday for giving an impassioned speech on the Senate floor.  “But I’m here on this floor to beg, to literally get down on my hands and knees to beg my colleagues, find a path forward here,” he said. “By doing something, we at least stop sending this quiet message of endorsement to these killers whose brains are breaking, who see the highest levels of government doing nothing shooting after shooting.”

Read more: Uvalde, Texas elementary school shooting spurs Sen. Chris Murphy to ask lawmakers ‘What are we doing? Why are we here?’

The White House announced that President Biden will deliver remarks on the “horrific news” at 8:15 p.m. ET on Tuesday, shortly after he returned to D.C. 

White House press secretary Karine Jean-Pierre tweeted that the president’s “prayers are with the families impacted by this awful event.” 

Former secretary of state and presidential candidate Hillary Clinton tweeted that “thoughts and prayers are not enough,” adding that “we are becoming a nation of anguish screams.” 

Among Republican leaders, Senate Minority Leader Mitch McConnell tweeted that he was “horrified and heartbroken” by the “disgusting violence directed at innocent schookids in Uvalde, Texas.” 

Texas Gov. Greg Abbott released a statement on the “horrific loss” saying that “Texans across the state are grieving for the victims of this senseless crime,” and he urged Texans to “come together to show our unwavering support to all who are suffering.” 

American poet Amanda Gorman, who became a household name after reading her own poem “The Hill We Climb” at President Joe Biden’s inauguration, tweeted that, “It takes a monster to kill children. But to watch monsters kill children again and again and do nothing isn’t just insanity — it’s inhumanity.”

Tuesday’s shooting is the 27th school shooting in the United States so far this year. And it comes less than two weeks after a gunman opened fire at a supermarket in Buffalo, New York, killing 10 Black shoppers and workers in what officials have described as a hate crime.

The Buffalo shooting led Biden to renew his push for an assault-weapons ban last week, although gun-control bills continue to face a tough road in the 50-50 Senate.