Texas school shooting: Suspect's grandmother upgraded to good condition

President Joe Biden addressed the nation Tuesday night following the mass shooting in Texas -- not even two weeks after he mourned victims of the mass shooting in Buffalo, New York.

"I’d hoped, when I became president, I would not have to do this again," Biden said. "Another massacre. Uvalde, Texas. An elementary school. Beautiful, second-, third-, fourth-graders."

"As a nation, we have to ask when in God's name are we going to stand up to the gun lobby," he said. "I am sick and tired of it -- we have to act."

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Connecticut Democrat Chris Murphy gave an impassioned argument on the Senate floor to his colleagues late Tuesday afternoon, hours after 21 were killed in the mass shooting.

"What are we doing?" Murphy asked the chamber. "There have been more mass shootings than days in the year."

"Our kids are living in fear every single time they set foot in the classroom because they think they're going to be next. What are we doing?"

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A fourth-grade teacher and a 10-year-old boy were among those killed, ABC News has learned.

The teacher, Eva Mireles, had worked in the school district for approximately 17 years, her aunt, Lydia Martinez Delgado, confirmed to ABC News.

Fourth-grader Xavier Lopez was among the 19 children killed.

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At least 21 people are dead after a gunman opened fire in Uvalde on Tuesday, authorities said.

Most of the victims were children in their last week of school before the summer break. Many other students and adults were injured in the mass shooting.

Here's what we know about what unfolded so far.