Iran severed diplomatic ties with the United States in 1979 and has been opposed to restoring them. For its part, the United States has offered to normalize relations on several occasions, but Iran has rebuffed all such offers. According to Tehran, Washington must first change its attitude toward Iran, a diplomatic way of saying the United States must accept the country as it is. But several other factors have informed Iran's obstinacy. Since the mid-1990s, Iran has been politically incoherent. Over the past 16 years, Supreme Leader Ayatollah Ali Khamenei has been at odds with Rouhani's two predecessors. He distrusted Mohammad Khatami's reformism, and he went through an outright power struggle with Mahmoud Ahmadinejad. During this time, Iran was thus unable or unwilling to negotiate substantively with the West.