For the first 73 Congresses, elections were held on the First Tuesday after the first Monday in November - but terms of the newly elected members did not begin until four months later. This was addressed by the 20th Amendment.
The Senate Committee on the Judiciary in its report suggested several reasons for the proposed Twentieth Amendment. It said in part:
“[W]hen our Constitution was adopted there was some reason for such a long intervention of time between the election and the actual commencement of work by the new Congress. . . . Under present conditions [of communication and transportation] the result of elections is known all over the country within a few hours after the polls close, and the Capital City is within a few days’ travel of the remotest portions of the country. . . ."
“Another effect of the amendment would be to abolish the so– called short session of Congress. . . Every other year, under our Constitution, the terms of Members of the House and one–third of the Members of the Senate expire on the 4th day of March. . . . Experience has shown that this brings about a very undesirable legislative condition. It is a physical impossibility during such a short session for Congress to give attention to much general legislation for the reason that it requires practically all of the time to dispose of the regular appropriation bills. . . . The result is a congested condition that brings about either no legislation or illy considered legislation. . . ."
“If it should happen that in the general election in November in presidential years no candidate for President had received a majority of all the electoral votes, the election of a President would then be thrown into the House of Representatives and the memberships of the House of Representatives called upon to elect a President would be the old Congress and not the new one just elected by the people. It might easily happen that the Members of the House of Representative, upon whom devolved the solemn duty of electing a Chief Magistrate for 4 years, had themselves been repudiated at the election that had just occurred, and the country would be confronted with the fact that a repudiated House, defeated by the people themselves at the general election, would still have the power to elect a President who would be in control of the country for the next 4 years. It is quite apparent that such a power ought not to exist, and that the people having expressed themselves at the ballot box should through the Representatives then selected, be able to select the President for the ensuing term. . . ."
This year, as has happened on previous occasions, January 3rd falls on a weekend. Congress therefore acted to set the start date on January 6th 2009.