US President Barack Obama denounced Tuesday what he called the \"sickening\" chemical weapons attack by Syrian forces in the Damascus suburbs, and said it posed a \"danger\" to US security. \"When dictators commit atrocities, they depend on the world to look the other way until those horrifying pictures fade from memory,\" Obama, making his case for military action, said in a much-anticipated televised address to the nation. \"The question now is what the United States of America and the international community is prepared to do about it,\" he added.