It has been a good week for President Obama — apart from the moment when Colonel Muammar Gaddafi called him “my son”. He has won the support of Russia, and maybe China, on pressing Iran to curb its nuclear ambitions. The remarks by President Medvedev were conditional, to be sure, but solid enough that Obama could stand smiling by his side and announce his success to the world. In opening the UN Security Council session yesterday he called for “the day when nuclear weapons have been banned”. He put this theme, toxically eccentric a few years ago, right at the...