<span>Euphemism is a mild or indirect word or expression substituted for one considered to be too harsh or blunt when referring to something unpleasant or embarrassing.</span>
~Hello there! ^_^
your question: Which official is the most powerful member of the White House..?
Your answer: The Chief of staff is the official that is the most powerful member of the White House. This person guides the White House staff.
~Hope this helps! :D