The Senate of the 107th Congress convened with 50 Democrats and 50 Republicans: until noon on 20 January 2001, Vice President Al Gore- a Democrat- remained in office and could theoretically break a party line tie vote; as a result, Senator Robert C. Byrd (Dem.- West Virginia) was elected Senate President pro Tempore on 3 January 2001. By prior arrangement between the Senate leadership of the two Parties: as of noon on 20 January 2001, when Dick Cheney- a Republican- took office as Vice President, after which he could theoretically break a party line tie vote, Senator Strom Thurmond (Rep.- South Carolina) became Senate President pro Tempore.

On 24 May 2001, Senator James Jeffords of Vermont, heretofore a Republican, announced his intention to become an Independent- making the Senate one of 50 Democrats, 49 Republicans and himself as the 1 Independent; this action resulted in Senator Byrd returning to the office of Senate President pro Tempore on 6 June 2001.