Donald Trump Jr. feuded with Sen. Jeff Flake, R-Ariz., on Twitter on Tuesday, saying the lawmaker "failed" to do his job and prevent the shooter responsible for the deadly church shooting in Texas from purchasing a firearm.

The dispute began after Flake tweeted about crafting a bill with Sen. Martin Heinrich, D-N.M., that would close loopholes and prevent those convicted of domestic violence from obtaining firearms.

"Incredibly proactive considering that law has been on the books since the mid 90s," the oldest son of the president responded to Flake.

"If being proactive means closing the #DomesticViolenceLoophole exploited by the #SutherlandSprings Texas shooter, you're right," Flake spat back.

"Wrong. Govt employees, like you, failed to do their job. He did a year for abuse & fracturing his kids scull. Should not have had a gun!" Donald Trump Jr. tweeted in response to Flake in a now deleted tweet.

Flake's bill is being crafted in response to the Texas church shooting on Sunday that took 26 lives and injured 20 other people.

Police said the shooter, Devin Kelley, used a Ruger AR-556 in the attack. Kelley served in the U.S. Air Force, but received a bad conduct discharge for assault against his ex-wife and stepson in 2012. It was also reported that Kelley briefly escaped from a mental health facility in New Mexico in 2012, but was soon found by police.

The U.S. Air Force said it failed to enter Kelley's domestic violence convictions into a federal crime database, an oversight which appears to have allowed him to purchase the gun used during the attack.