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What are the two responsibilities given to the Vice President in the Constitution?
Jefferson, Madison, Jackson, Lincoln, Grant, Cleveland, McKinley, and Nixon all had different vice-presidents during their second terms. Franklin Roosevelt changed veeps for his third term and again...
I'm not sure what they all are, but he (or she) is there to cast a tie-breaker if a vote ends up 50-50. He (or she) probably calls the senate to order, and collects the money for lunches or whatnot...