But this response does not obviate the fact that US decision makers are trusting in the authority of Rouhani and Zarif. The Boston Globe reported that in a particularly heated exchange during the endgame in Vienna, Kerry demanded to know from Zarif: 'Do you have the authority to negotiate this deal and bring it to closure?' Zarif reportedly confirmed that he did. The authority question, and the issue of trust that resides in it, bears crucially on how far the lead Iranian negotiators retain the confidence – and indeed the trust – of Iran’s chief nuclear decision maker, the Supreme Leader, Ayatollah Ali Khamenei. In previous negotiations, it has been the Supreme Leader who has pulled the plug on any prospective agreement (eg, the 2009 fuel swap proposal), and retaining his support is crucial to the implementation of the agreement.