Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeRepublican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style Bush endorsing Biden? Don't hold your breath MORE (R-Ariz.) on Sunday pushed back on the White House's characterization that President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE was joking when he called Democrats "treasonous" for not clapping at the State of the Union, saying the president's comments are not a joking matter.

"I don't think it's a joking matter to say that somebody is treasonous, and he ought to stop it," Flake told NBC's Chuck Todd on "Meet the Press."

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"Words matter," the Republican senator, who recently announced his retirement, said. "When he talks about fake news, for example, I gave another speech about how that gives aid and comfort to authoritarians around the world who are now labeling their opposition or dismissing real dissent as fake news.

"So these things matter."

Flake has often criticized the president. Earlier this month, he ripped Trump after the president suggested it was treason for Democrats not to applaud during his State of the Union speech, saying the remarks were "not normal."

"One who levels such a charge knows neither the meaning of treason nor the power that the words of a president carry. ... Our silence will also mark the day that we failed to recognize that this conduct in an American president is simply not normal," the senator said during a speech on the Senate floor.