(CNN) Republican Sen. Jeff Flake announced Wednesday he's backing a bill to increase the minimum age to buy a semi-automatic rifle, lending bipartisan support to legislation that was introduced last week by Democratic Sen. Dianne Feinstein in the wake of the mass shooting at a high school in Parkland, Florida.
"A kid too young buy a handgun should be too young to buy an #AR15," Flake, of Arizona, said in a tweet. "Working with @SenFeinstein on a bipartisan bill that will raise the minimum purchase age for non-military buyers from 18 to 21 - the same age you currently have to be to purchase a handgun."
The idea has emerged as potential compromise among GOP and Democratic lawmakers -- who are sharply divided and therefore gridlocked on gun control issues -- as they search for a response to killings by 19-year-old Nikolas Cruz, a former student at the school. Cruz used an AR-15 style weapon, which he purchased legally, to kill 17 people.
They are also considering a bipartisan bill to improve reporting compliance by states and federal agencies to the National Instant Criminal Background Check System.
"Under current law, licensed gun dealers cannot sell a handgun to anyone under 21, but they are allowed to sell assault rifles like the AR-15 to anyone over 18. This policy is dangerous and makes absolutely not sense," Feinstein of California said when introducing her bill last week. "If you can't buy a handgun or a bottle of beer, you shouldn't be able to buy an AR-15."
Flake announced last fall he would not seek re-election for his Senate seat.
At a White House forum Wednesday on school shootings with parents, teachers and student survivors of recent tragedies, President Donald Trump was urged to consider raising the age at which such weapons could be purchased, something he appeared to embrace.
"In addition to what we're going to do about background checks, we're going to go very strong into age, age of purchase, and we're also going to go very strong into the mental health aspect," Trump said.
But the measure ran into powerful headwinds Wednesday evening, when the National Rifle Association announced it rejects lifting the age for purchasing rifles.
"Federal Law prohibits adults under the age of 21 from purchasing a handgun from a licensed firearm dealer. Legislative proposals that prevent law-abiding adults aged 18-20 years old from acquiring rifles and shotguns effectively prohibits them for purchasing any firearm, thus depriving them of their constitutional right to self-protection," said Jennifer Baker, the NRA public affairs director.
Baker added: "We need serious proposals to prevent violent criminals and the dangerously mentally ill from acquiring firearms. Passing a law that makes it illegal for a 20-year-old to purchase a shotgun for hunting or an adult single mother from purchasing the most effective self-defense rifle on the market punishes law-abiding citizens for the evil acts of criminals."