The concept of seniority in the Senate developed through the institution's first half-century. In its earliest decades, the Senate struggled to find an equitable means for distributing special status among members. Who would serve as president pro tempore in the absence of the vice president? Who would chair the important committees? Who would obtain desirable office space?
Initially, the Senate conducted numerous and time-consuming roll-call votes to determine committee assignments. By the 1840s, a time of rapid membership turnover and short tenures in office, the Senate began recognizing seniority of service in arranging committee rosters.
In 1858, however, the Senate briefly ignored seniority when its Democratic caucus removed Stephen Douglas as chairman of the significant Committee on Territories because he did not reflect the party's views on slavery. This departure from tradition–along with the 1871 removal of Charles Sumner as chairman of the Foreign Relations Committee for opposing an annexation treaty favored by the president–created hard feelings within the Chamber and banner headlines in papers across the nation.
In later years, the Senate occasionally adjusted its committee seniority rules–most notably in 1997 when the Senate Republican Conference placed six-year term limits on its party's committee chairmen and ranking members.
Baker, Richard A. The New Members' Guide to Traditions of the United States Senate. (Washington, GPO, 2006. S.Pub. 109-25), 6.