Obama's Nawroz message to Iran marked a serious shift in American policy and attitude towards Iran but also showed the structural weaknesses in the American state that could prevent it from achieving those goals. Khamenei, the Supreme Leader, gave an excellent and well-thought-out reply to that speech the following day, which has been analysed by Juan Cole and Farideh Farhi. When discussing countries like Turkey, Iran, and Pakistan, commentators often mention the existence of a 'deep state', a coterie of officials somewhere within the state apparatus who have ultimate control over policy. I don't think this is much the case with Iran, and I'll explain below, but it definitely is a factor with the US, and in a lot of ways it gets to the heart of constraints on nation-states' abilities to act and react.
"You, too, have a choice. The United States wants the Islamic Republic of Iran to take its rightful place in the community of nation. You have that right -- but it comes with real responsibilities, and that place cannot be reached through terror or arms, but rather through peaceful actions that demonstrate the true greatness of the Iranian people and civilisation. And the measure of that greatness is not the capacity to destroy, it is your demonstrated capacity to build and create."