In its rush to stand up an overnight democratic success story, the Bush administration overlooked Afghan history. Indeed, it was willfully ahistorical. That's tragic, because Afghan history demonstrates conclusively and beyond dispute that legitimacy of governance there is derived exclusively from Weber's first two sources: traditional (in the form of the monarchy and tribal patriarchies) and religious. Either there has been a king, or religious leadership, or a leader validated by the caliphate (or afterwards by indigenous religious polities).
Often in Afghan history, legitimacy thus derived has been reinforced by other means, usually coercive and often brutal. For example, the rule of Amir Abdur Rahman, "The Iron Amir," (1880-1901) and that of the Taliban (1996-2001) were predicated on accepted sources of legitimacy of governance (dynastic and religious, respectively), but reinforced by totalitarian methods. These two examples make the point that legitimacy should not be conflated with popularity: having the authority to rule is quite distinct from being a popular ruler. American presidents, for example, are always legitimate leaders but not always popular ones.
This historical reality poses a major problem for the US. Democracy is not a coat of paint. A feudal society in which women are still largely treated as property and literacy hovers below 10 percent in rural areas does not magically shortcut 400 years of political development and morph into a democracy in a decade. The current government of Afghanistan's claim to legitimacy is based entirely on a legal source – winning an election. Yet this has no historical basis for legitimizing Afghan rule. The winner of today's election will largely be seen as illegitimate he is elected.