No one disputes that America has great leaders. However, perhaps you will agree with me that of late, the USA has been unfortunate in its crop of leaders, with the exception of probably Obama (my personal opinion and it is much too early to give a proper assessment of his presidency). The USA is by means unique in this melancholy phenomenon; you only have to look at what is happening in my own backyard, the UK. Please take a look at my best effort at explaining what is happening to us, in a response I have given to: https://thinkprogress.org/al-gore-part-i-29163bf6f22
It is not a perfect response as I have written it in haste, but it may give you a clue as to my thinking.