The Vice President of the United States has a very specific job.
One of the key factors given to him is that under the Constitution, the Vice President is President of the United States Senate.
In that capacity, he or she is allowed to vote in the Senate when necessary to break a tie. While Senate customs have created supermajority rules that have diminished this Constitutional power, the Vice President still retains the ability to influence legislation (e.g. the Deficit Reduction Act of 2005).
Pursuant to the Twelfth Amendment, the Vice President presides over the joint session of Congress when it convenes to count the vote of the Electoral College.
While the Vice President’s only constitutionally prescribed functions aside from Presidential succession relate to his role as President of the Senate, the office is commonly viewed as a component of the executive branch of the federal government. The United States Constitution does not expressly assign the office to any one branch, causing a dispute amongst scholars whether it belongs to the executive branch, the legislative branch, or both. The modern view of the Vice President as a member of the executive branch is due in part to the assignment of executive duties to the Vice President by either the President or Congress, though such activities are only recent historical developments.