Tehran hoped for dragging United States into some acute crisis as it announced in a provocative way the building of 10 new additional nuclear enrichment centres in order to urge the United States to make a step backward for fear of a conflict. Under Bush, we would have assisted in some escalation but presently nothing happened. Obama didn’t make any big statement : he mentioned the possibility to reinforce sanctions right before he called for the dialogue’s continuation in parallel with the sanctions that are already implemented. Such reaction cast a chill over the provocative ardours of the mullahs who find it difficult to make the right answer. Are they so disappointed to the point of renouncing to their policy of deliberate provocations ? To know it, it’s necessary to review the background history of the chaotic relations between Tehran and Washington.