Beto O'Rourke, who is the Democrat running for governor in Texas, interrupted a press briefing about the shooting at Robb Elementary in Uvalde.
Texas Gov. Greg Abbott had finished commenting about mental health resources for the community and introduced the lieutenant governor when O'Rourke approached the table and began shouting.
O'Rourke told Abbott that he has done "nothing" to protect Texans following other mass shootings in the state.
A person could be heard saying, "You're out of line," as O'Rourke continued shouting.
Security at the event eventually ushered O'Rourke away from the table and he left the auditorium.
Abbott reflected on O'Rourke, calling for all Texans to come together.
Speaking with reporters outside, O'Rourke said that leaders "owe" the parents of mass shooting victims.
He said the state should require universal background checks and stop selling AR-15s, which the gunman reportedly used in the shooting at Robb Elementary.