Ibn Tayyar

Al-Salamu Alaykum
Question to brother @Islamic Salvation. 
Is it not true that someone is considered a kafir if he knowingly denies something that is a part of the Deen - if he has come to know about its Revelation? 
For example, if someone had denied any hukm - even a simple one, that had come from the words of the Prophet (saww), without any shubha or excuse, then he has in essence denied a Revelation, and has thus become a kafir. Can this not be the case with those who rejected the Wilaya after the incident of Ghadeer, something which they witnessed with their own eyes and heard with their own ears?
Or perhaps those who rejected Imam Ali (عليه السلام) knew that he was worthy of it, and therefore didn't deny the Wilaya, but simply took Khilafa for dunyawi purposes, making them transgressors or perhaps hypocrites, but not outwardly kafir - this is the answer I have gotten. 
But it would be interesting to hear your insight brother. Thanks.