President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE on Sunday put blame on former President Obama after the alleged chemical attack in Syria.

"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!" Trump tweeted, referring to Syrian President Bashar Assad.

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

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Obama said last year that he believed his decision to negotiate rather than respond with force to Syria’s use of chemical weapons required some of the greatest “political courage” of his presidency.

That was despite Obama saying in 2012 that if Assad used chemical weapons it would cross “a red line” with the U.S. The United Nations accused Syria of using chemical weapons on its own people in 2013.

“You generally get praised for taking military action, and you’re often criticized for not doing so,” Obama said last May.

Dozens died and hundreds were reported injured Saturday in an alleged chemical attack in Syria.

State Department spokesperson Heather Nauert said in a statement that U.S. officials are closely following the “disturbing reports … regarding another alleged chemical weapons attack, this time targeting a hospital in Douma, Syria.”

The U.S. is calling on Russia to end its support for Assad.

Damascus has denied responsibility for the attack, Reuters reported.

Trump administration officials told The Associated Press in February they believed forces loyal to Assad might have been in the process of working on new, or more refined chemical weapons.

Trump said last year that reports of a deadly gas attack by forces loyal to Assad had “crossed a lot of lines.”

— Updated 9:30 a.m.