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In the wake of a suspected chemical attack in Syria that killed dozens, President Trump slammed former President Barack Obama for not crossing his stated "red line" with Syrian President Bashar Assad.

Trump made the comments on Twitter following the attack in the town of Douma amid a resumed offensive by Syrian government forces.

Trump also vowed that there will be a "big price to pay," calling out Russian President Vladimir Putin and Iran for backing Assad, whose forces are believed to have carried out the attack.

On "Fox & Friends" on Sunday, Alan Dershowitz said Trump has "no choice" but to respond, and he must not make the same "tragic mistake" Obama did.

Obama vowed in 2012 that chemical attacks by Assad's regime would cross a “red line," but he later failed to enforce the promise when hundreds of Syrians were killed by sarin gas.

Dershowitz, a lifelong Democrat, said Obama's lack of action created a power vacuum in Syria, emboldening Assad and essentially inviting Russia and Iran to play more prominent roles in the Syrian civil war.

"These deaths are horrible and tragic. ... Deliberate, willful targeting of women and children. The United States has to do something about it. We're the only game in town," Dershowitz said. "We have an obligation in the name of humanity to prevent these killings from taking place."

"I think this president will stand strong against that. And I hope he can stop this guy. Nobody else has stopped him."

Watch more above.

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