An 18-year-old perpetrator attacked a classroom at Robb Elementary School in Texas, USA, on Tuesday morning, local time.
He shot dead at least 19 children and two adults.
Several children are still being cared for in hospital.
And Democrat Beto O'Rourke, who is running for governor of Texas, says he wants strong action.
Interrupted the governor
During a press conference about the school shooting, he interrupted Republican Gov. Greg Abbott.
- The time to stop the next shooting is now and you do nothing, he said.
Thrown out
Despite the fact that Beto O'Rourke was ordered to sit down, he continued and in the end he was thrown out.
- I want us to do something immediately.
If we continue to accept this, then it's not just the governor's fault.
Then it is also ours.
I will not accept this.
That's why I'm here, he said.
Pope: "My heart is broken"
The outside world reacts strongly after the act.
During a performance on Wednesday, the pope said that "my heart is broken".
Several leaders have also expressed their condolences.
Including German Chancellor Olaf Scholz.
"Our thoughts go out to the injured and the mourners of the victims of this inconceivable massacre for which there are hardly any words," he wrote on Twitter.
Sweden's Foreign Minister Ann Linde (S) writes that her thoughts are with friends and family of those affected by the terrible attack.