Monday 9 September, 2013, was the worst day for US and wider Western diplomacy since records began.At the Foreign Office here in London we had the bizarre spectacle of US Secretary of State John Kerry giving a businesslike account of diplomatic incentives: If one party believes that it can rub out countless numbers of his own citizens with impunity using chemicals that have been banned for nearly 100 years because of what Europe learned in World War I, if he can do that with impunity, he will never come to a negotiating table … If you don’t draw those lines,...