Outspoken Democrats -- from far-left "Squad" members to 2020 presidential hopefuls -- wasted little time Saturday in denouncing President Trump's warning to Iran about possible retaliation for the U.S. airstrike that killed Iran's Gen. Qassem Soleimani.

Rep. Alexandria Ocasio-Cortez, D-N.Y., answered by calling the president a “monster.”

“This is a war crime," Ocasio-Cortez wrote. "Threatening to target and kill innocent families, women and children -- which is what you’re doing by targeting cultural sites - does not make you a ‘tough guy,’ It does not make you ‘strategic.’ It makes you a monster.”

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Rep. Ilhan Omar, D-Minn., accused Trump of "threatening to commit war crimes." "God help us all!" she added.

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Presidential candidate Sen. Elizabeth Warren, D-Mass., expressed a similar message.

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“You are threatening to commit war crimes," Warren wrote. "We are not at war with Iran. The American people do not want a war with Iran. This is a democracy. You do not get to start a war with Iran, and your threats put our troops and diplomats at greater risk. Stop.”

Former Vice President Joe Biden accused the president of "irrational" behavior.

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“The more the walls close in on this guy, the more irrational he becomes,” Biden wrote.

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In his message Saturday, Trump had warned Iran that the U.S. had already identified 52 sites in the country that its military could target in the event of a retaliatory Iranian strike against the U.S.

Iranian Supreme Leader Ayatollah Ali Khamenei had said "harsh retaliation is waiting” for the United States after Trump ordered an airstrike that killed Soleimani in Baghdad early Friday.