Sen. Jeff Flake, R-Ariz., criticized President Trump on the Senate floor Tuesday after Trump suggested Monday that Democrats who refused to stand up and applaud him during his State of the Union address were guilty of treason.

The White House said Tuesday Trump was joking, but Flake said there's nothing funny about treason, or the way Trump was trying to accuse Democrats of treason.

"Treason is not a punchline, Mr. President," Flake said. He said Trump appears to not know what he's talking about, or how his words will be heard in the country and around the world.

"One who levels such a charge knows neither the meaning of treason nor the power that the words of a president carry," he said.

"And if we are numb to such words, then we will surely regret that we failed to defend our colleagues in the Congress against such a vile remark," Flake said. "But our silence will also mark the day that we failed to recognize that this conduct in an American president simply is not normal."

On Monday, Trump noted that "somebody" suggested Democrats were treasonous for not applauding after Trump noted the sharp drop in black unemployment levels. "Can we call that treason? Why not?" he asked.

But Flake said Trump misunderstands why people stand and clap during State of the Union addresses.

"Mr. President, respect is earned, not commanded," he said. "Applause signals approval of an idea, not loyalty toward one's country."