The ceasefire in the Gulf is four weeks old and showing its age. The US and Iran's determination to keep the pressure on each other has put it in serious jeopardy. This is a dangerous moment. The ceasefire opened up a chance for diplomacy that looked for a short time as if it might make progress. Americans and Iranians faced each other across a conference table in Pakistan's capital, Islamabad, but came away empty-handed. The Pakistanis are trying to revive the process, without much success so far. Both America and Iran want to have a deal. But they have different...