Massie challenged unconstitutional gun-control measures that are sweeping the nation by introducing a bill that would lower the age limit for buying a handgun. 

Via Guns.com: 

A Kentucky Republican has introduced a measure that flips the argument on current trending gun control legislation by holding the age to buy any gun in the U.S. should be dropped to 18.

U.S. Rep. Thomas Massie has proposed H.R. 5112 which would reduce, from 21 to 18, the minimum age at which someone can obtain a handgun from a licensed gun dealer. The move is the polar opposite of recent proposals backed by gun control advocates, various lawmakers and even for a time President Trump, to raise the age for gun purchases from 18 to 21.

“If you raise the age to buy a long gun from 18 to 21 while keeping the age to buy a handgun at 21, you have completely extinguished the constitutionally guaranteed right of 20-year-old mothers to keep and bear arms,” said Massie on social media. The lawmaker, chair of the Congressional Second Amendment Caucus, made the same argument last Sunday on Meet the Press.

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