 Behind this is former service as a senator (only giving the senator seniority within his or her new incoming class), service as vice president, a House member, a cabinet secretary, or a governor of a state.The final factor is the population of the senator's state.Senators who were sworn in during the middle of the two-year congressional term (up until the last senator who was not sworn in early after winning the November 1960 election) are listed at the end of the list with no number.