US President Donald Trump has lashed out at the Syrian President Bashar al-Assad and his allies Russia and Iran over a suspected chemical attack, saying there will be a "big price to pay". In a series of tweets, Mr Trump described President Assad as an "animal" and said it was a sick attack. Medical sources say ninety people were killed in an attack on the rebel-held town of Douma on Sunday. Both Syria and Russia deny a chemical attack took place. Senior White House reporter for Politico Josh Gerstein discusses the reaction with Susie Ferguson.