WASHINGTON (Reuters) - Some U.S. Republican lawmakers joined their Democratic colleagues on Tuesday in criticizing President Donald Trump for labeling them as “treasonous” and “un-American” in response to the cold reception they gave him during his State of the Union address last week.

“Well, that borders on divisive,” the second-most powerful Democrat in the Senate Dick Durbin told reporters in a purposefully understated tone.

Speaking at a manufacturing plant in Ohio on Monday, the Republican president said Democrats “would rather see Trump do badly than our country do well.”

“They were like death and un-American,” he said of Democrats who sat stone-faced, robed in black in solidarity with victims of sexual misconduct, as he heralded the economy’s achievements in his address a week ago to a joint session of Congress.

“Somebody said ‘treasonous.’ I mean, eh. I guess, why not? Can we call that treason, why not?,” he said.

The remarks sparked a firestorm of criticism from Democrats on Capitol Hill.

Senator Tammy Duckworth quoted President Theodore Roosevelt in a response on Twitter.

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“‘To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public,’” she tweeted.

White House spokesman Hogan Gidley said the remarks on treason - an offense punishable by death - were offered as tongue-in-cheek.

“The president was obviously joking. But what’s serious is the Democrats seem to put their personal hatred for this president above their desire to see America succeed,” he said in a statement.

But Democrats weren’t the only critics.

“Treason is not a punch line, Mr. President. Applause is approval of an idea, not loyalty to one’s country,” said Senator Jeff Flake, a Republican who frequently reproaches Trump and his policies, in a blistering attack on the Senate floor on Tuesday. “Our Democratic colleagues love this country as much as we do. To suggest otherwise is simply unconscionable.”

Even Representative Mark Meadows, a leading Republican conservative closely allied with Trump, took issue with the president’s comments. “Certainly saying that someone’s un-American because of their unwillingness to clap is not something that most Americans would agree with,” he said on CNN.

But Republican Representative Claudia Tenney, also speaking about Democrats on CNN on Tuesday, said “I would say it was un-American, and they don’t love our country. I don’t know if I would go as far as treasonous, but the president is before a large audience and he likes to talk in colorful language.”