The father of a Parkland shooting victim bashed President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE on Tuesday night, calling him a liar for backing away from support for background checks on gun purchases.

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“What he did today with his arguments against gun safety, that’s who he is, he’s a liar," said Fred Guttenberg, whose 14-year-old daughter Jaime was killed during the February 2018 mass shooting at Marjory Stoneman Douglas High School in Parkland, Fla.

Guttenberg, who frequently speaks out for gun control, made the comments during an interview with Chris Matthews on MSNBC's "Hardball."

“He did the same thing after Parkland. It’s who he is, he’s a liar, he can’t be taken seriously,” Guttenberg said.

Trump on Tuesday said that America already has “very strong background checks” for purchasing guns and increased gun control legislation could lead to a “slippery slope” where “everything gets taken away.”

He made the remarks after a phone conversation with National Rifle Association (NRA) CEO Wayne LaPierre. LaPierre in a tweet Tuesday confirmed he spoke with Trump.

Guttenberg hammered Trump's assertion about a "slippery slope."

“A slippery slope is getting to 40,000 [gun violence] victims a year,” he said. “Wanting to do something about it, and wanting to defeat these people, and wanting to get Wayne LaPierre out of the president’s ear … is simply wanting to be responsible and fix this.”

He added that the "slippery slope" is "the ultimate NRA talking point."

Trump initially expressed support for addressing background checks following back-to-back mass shootings earlier this month in El Paso, Texas, and Dayton, Ohio, that killed more than 30 people in total.