Why?

 Why a Vice President would like to become a President?

First you have to background check the candidates first for Vice President. Background check the family, education, heritage, culture and tradition.

Usually, VP aiming for Presidency is about challlenges or aiming for higher power.

Sometimes its about personal claim or personal vendetta.

If its personal vendetta it will never be successful. That person could succeed only if he or she is corrupt or because she is backed up by other elements of graft and corruption with the same purpose. 

Personal vendetta is a "mortal sin."

That's all. Where I got this idea? I read too much WORLD HISTORY and watch documentary.