After the Messenger of Allah, Abu Bakr seized Caliphate. He and his followers claimed that since he was unanimously elected by the Muslims, he was the righteous leader of the Ummah. 
 

Yet, with little reflection upon the matter of Caliphate, one realizes that it is an extension and continuation of the Prophethood without revelation. Thereupon, since Prophethood can only be assigned to someone through Divine specification, likewise Caliphate cannot be assigned to anyone by mankind; rather, it is a Divine code bestowed upon men by Divine specification. 
 

Moreover, this consensus that Abu Bakr and his followers claim to have achieved is not valid; because the Ansar, Bani Hashim, Ammar, Salman, Miqdad, Abu Dhar and many other companions opposed the election of Abu Bakr to the Divine post, which was previously granted to Ali (A). Nevertheless, Abu Bakr was able to seize power and eradicate Ali's (A) and his followers attempts to regain his righteous post.