Use stream of consciousness to answer the following. The U.S. Constitution also provides for appointment of one of the elected Senators to serve as President pro tempore. This Senator presides when the vice president was absent from the body. The President pro tempore is selected by the body specifically for the role of presiding in the absence of (as the meaning of pro tempore, literally "for the time being") the actual presiding officer. By tradition, the title of President pro tempore has come to be given more-or-less automatically to the most senior senator of the majority party. In actual practice in the modern Senate, the President pro tempore also does not often serve in the role (though it is his or her constitutional right to do so), instead, as governed by the aforementioned Rule I, he or she frequently designates a junior senator to perform the function.

Answer this question based on the passage: who is the backup leader of the senate?
The relevant information is: The President pro tempore is selected by the body specifically for the role of presiding in the absence of (as the meaning of pro tempore, literally "for the time being") the actual presiding officer. Final answer: The President pro tempore.