President Trump’s proposal to raise the minimum age for buying a long gun to 21 would fail in the Senate, the body’s No. 2 Republican has warned, arguing that such a measure would not save lives.

“What we want to focus on is things that will actually save lives,” Senate Majority Whip John Cornyn of Texas told CNN late Friday.

In a tweet Thursday, Trump backed raising the federal minimum age for purchasing long guns to 21 from the current 18.

Nikolas Cruz, who legally bought the AR-15 he used in the slaughter at Marjory Stoneman Douglas HS in Parkland, Fla., is 19 years old.

A minimum age of 21 “would be difficult to enforce” and does not attack “the root of the problem,” Cornyn said.

Cornyn instead pushed the bipartisan Fix NICS Act, which aims to reinforce the National Instant Criminal Background Check System, the FBI system used to verify whether a person is eligible to buy guns.

The act would punish agencies that do not send disqualifying information to the FBI and award cash to states that improve their participation.

A group of 19 moderate House Republicans — including Reps. Dan Donovan (SI) and Peter King (LI) — wants Speaker Paul Ryan to bring a version of the bill up for a vote Monday.