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President Donald Trump on Sunday strongly condemned what he described in tweets as a "mindless CHEMICAL attack in Syria" that allegedly left women and children dead.

He laid the blame squarely at the feet of Russian President Vladimir Putin, Russia and Iran for backing resident Bashar al-Assad, who he called an "animal." Trump also warned, "Big price to pay."

"Open area immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK!" the president wrote.

If President Obama had crossed his stated Red Line In The Sand, the Syrian disaster would have ended long ago! Animal Assad would have been history! — Donald J. Trump (@realDonaldTrump) April 8, 2018

In the third of a series of tweets, he faulted former President Barack Obama for not intervening in Syria during his time in office. In April of last year, Trump ordered a Tomahawk missile strike against a Syrian airbase for a similar chemical attack.

Sunday's posts left many wondering if Trump would potentially retaliate against the Syrian government, which is backed by Russia. The criticism of Putin is arguably his strongest critique of Russia since he took office 442 days ago.

Syrian aid groups and activists allege that dozens of people died in a suspected chemical weapons attack on the city of Douma, the last rebel stronghold in eastern Ghouta where Assad has pursued an intensive bombing campaign.

The Syrian American Medical Society said that more than 500 cases, mostly women and children, suffered symptoms “indicative of exposure to a chemical agent” and 42 were reported dead.

Both Syria and Russia deny involvement in Sunday’s alleged chemical attack.

Homeland Security adviser Tom Bossert said on ABC’s “This Week” on Sunday that the White House is considering how to respond. He added that the national security team had been speaking to the president “all throughout the evening and the morning.”

“I wouldn’t take anything off the table,” he said.

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The State Department, meanwhile, provided a full-throated critique of Russia in a statement on Saturday night that claimed that the nation had “breached its commitments to the United Nations” and called “into question [Russia’s] commitment to resolve the overall crisis and to larger non-proliferation priorities.”

“Russia, with its unwavering support for the [Assad] regime, ultimately bears responsibility for these brutal attacks, targeting of countless civilians, and the suffocation of Syria’s most vulnerable communities with chemical weapons,” State Department spokesperson Heather Nauert said.

Last week, Trump reluctantly agreed to keep U.S. troops in Syria, though he stressed to his national security team his desire to end U.S. involvement in the conflict as soon as possible.

Politicians call for action after Syria's alleged chemical attack

Republican and Democrat leaders decried the alleged chemical attack on Sunday, calling for the U.S. to hold the Assad government accountable.

Sen. Lindsey Graham, R-S.C., who serves on the Armed Services Committee called on the White House to act.

“If [the president] doesn’t follow through and live up to that tweet, he’s going to look weak in the eyes of Russia and Iran,” Graham said on ABC’s “This Week” on Sunday. “This is a defining moment.”

Others from the president's own party piled on.

Sen. Susan Collins, R-Maine, said on CNN's "State of the Union" that Trump should rethink his plans for an early withdrawal from Syria and consider another targeted attack on Syria's military facilities, such as the one he ordered a year ago.

"That may be an option that we should consider now," she said. "But it is further reason why it is so important that the president ramp up the pressure and the sanctions on the Russian government, because, without the support of Russia, I do not believe that Assad would still be in office."

Sen. John McCain, R-Ariz., also blasted the president, as he said Trump signaling last week that the U.S. would withdraw from Syria only served to embolden Assad, Russia and Iran to conduct the attack.

While McCain said it was good that Trump criticized all three parties on Twitter, he said social media posts meant little in this situation.

"The question now is whether he will do anything about it," he said. "The President responded decisively when Assad used chemical weapons last year. He should do so again, and demonstrate that Assad will pay a price for his war crimes."

In the House, Republicans were also riled up and Speaker of the House Paul Ryan, R-Wis., said that the United States should continue to lead in holding Assad and Russia accountable.

The chemical attack in Syria is a horror that cannot be tolerated by responsible nations. The U.S. must continue to lead an international effort to hold the Assad regime and Russia accountable for their actions. — Paul Ryan (@SpeakerRyan) April 8, 2018

Rep. Michael McCaul, R-Texas, who serves as chair of the House Homeland Security Committee voiced his agreement on Fox News and called for military action.

“We’re not going to occupy countries anymore, but this cannot stand in the civilized world,” McCaul said. “This needs to be responded to in a very firm and strong way. I think we need to deal also with Russia and Iran’s involvement in this. I think they are complicit.”

Democrats also called for the White House to act and coordinate an international response.

Sen. Ben Cardin, D-Md., said on CBS's "Face the Nation" that "President Assad needs to be held accountable for his war crimes."

"We need to make sure that there is a proceeding started by the international community to hold him accountable," said Cardin, who serves on the Senate Foreign Relations Committee. "This is not the first use of chemical weapons."

House Minority Leader Nancy Pelosi, D-Calif., said that Putin needed to be held accountable for the alleged attack as he had enabled "these war crimes." But how to do that rests with the White House, she added.

“Members of Congress expect a comprehensive intelligence briefing on this attack as soon as possible," she said in a statement. "The Trump Administration must finally provide a smart, strong and consistent strategy in Syria.”

Sen. Bob Menendez, D-N.J., said it could affect Mike Pompeo, who Trump nominated to replace Rex Tillerson as secretary of state, as he enters Senate confirmation hearings this week.

“The United States must not waiver in our utter rejection of the use of chemical weapons anywhere in the world, by anyone, for any reason," Menedez said in a statement. "During his upcoming hearing, I expect Secretary of State-nominee Pompeo to articulate an actual policy for Syria.”