Simplify the following text for a Grade 7 native English-speaking person.
Original: The President pro tempore ( or ; also referred to as President pro tem ) is the second-highest-ranking official of the United States Senate and the highest-ranking Senator .
Simplified: Daniel Inouye ( D-HI ) is the President pro tempore . When the Vice President can not be in charge , the President pro tempore is in charge of the Senate .