Donald Trump, the US president, has warned Russia’s Vladimir Putin that there would be a “big price to pay” for a suspected Syrian chemical weapons attack that killed 70 people, including children. In his harshest criticism of the Russian leader since taking office, Mr Trump said Mr Putin was partly “responsible” for the attack on rebels in Douma, a town in Eastern Ghouta. The US president also criticised Barack Obama’s failure to police a “red line” over chemical weapons, while a senior White House official said no form of response was “off the table”. The comments raise the possibility of...