 Casey, Klobuchar, Whitehouse, and Tester rank in that order because as of the 2000 census, Pennsylvania, Minnesota, Rhode Island, and Montana had populations that ranked in that order, so Tester is ranked 33rd in seniority when the 116th United States Congress convened.Only relevant factors are listed below.For senators whose seniority is based on their state's respective population, the state population ranking is given as determined by the relevant United States Census current at the time that they began service.