The fact that the gunman responsible for this week’s massacre in Uvalde was able to buy two AR-15s days after his 18th birthday highlights how much easier it is for Americans to purchase rifles than handguns.

Under federal law, Americans buying handguns from licensed dealers must be at least 21, which would have precluded the gunman from buying that type of weapon. That trumps Texas law, which only requires buyers of any type of firearm to be 18 or older.

Following Tuesday’s massacre at Robb Elementary School, which killed 19 children and two adults, a growing number of lawmakers in Texas and beyond are calling for the minimum age to purchase assault rifles to be raised to 21 from 18. Doing so would require undoing nearly two centuries of more permissive regulations on so-called long guns.

“It’s something that could happen at either the state or federal level, but I don’t see movement on either front,” said Sandra Guerra Thompson, a criminal law professor at the University of Houston Law Center.

Only six states — Florida, Washington, Vermont, California, Illinois and Hawaii — have increased the minimum purchase age for long guns to 21, according to the Giffords Law Center to Prevent Gun Violence. The majority did so following the 2018 massacre in Parkland, Florida, where a then-19-year-old assailant killed 17 people at a high school.