Beto O'Rourke pledges to take away Americans' AR-15s. A Texas lawmaker is being accused of making a death threat in response.

A Texas Republican lawmaker is under fire after issuing a controversial response to presidential candidate Beto O'Rourke's campaign promise to take away Americans' AR-15s.

O'Rourke, a former Democratic representative from Texas, made the remarks during Thursday night's Democratic debate in Houston.

What happened?

Texas state Rep. Briscoe Cain addressed O'Rourke's remarks on Twitter, using the presidential candidate's legal name in his response.

"My AR is ready for you Robert Francis," Cain wrote.

During Thursday's debate, O'Rourke said that the AR-15 and the AK-47 are weapons "designed to kill people on a battlefield," and vowed to remove them from the American public if elected.

"In Odessa [Texas], I met the mother of a 15-year-old girl who was shot by an AR-15, and that mother watched her bleed to death over the course of an hour because so many other people were shot by that AR-15 in Odessa and Midland [Texas]," O'Rourke said, referring to the mass killing that took place in August when a suspect began indiscriminately firing on people walking the streets.

"Hell yes we're going to take your AR-15, your AK-47," O'Rourke promised. "We're not going to allow it to be used against our fellow Americans anymore."

O'Rourke took notice of Cain's remarks on Twitter and fired back. He took a screenshot of Cain's initial tweet and wrote, "This is a death threat, Representative. Clearly, you shouldn't own an AR-15 — and neither should anyone else."

What else?

Twitter ended up removing Cain's remark from the social media platform for violating its rules and terms of service.

After Twitter removed the tweet, Cain responded to O'Rourke's remark.

"You're a child Robert Francis," wrote Cain, who hails from Harris County, Texas, and is the state representative for District 128. .

Democratic Rep. Eric Swalwell (Calif.) later defended O'Rourke from Cain's inflammatory tweet.

He wrote, "If your response to a candidate proposing a new gun law is threatening to kill the candidate, you have proved exactly why we need tougher gun laws. @BriscoeCain should be red-flagged and disarmed."