lame duck: an office holder who has not been re-elected
The original lame ducks were unfortunate speculators who had lost their shirts on the stock exchange. This usage is first mentioned in print in a letter written by Hugh Walpole in 1761: "Do you know what a Bull, a Bear, and a Lame Duck are?" A book about Wall Street written in 1870 further elaborates: "The 'Lame Duck' is a broker who has failed to meet his engagement; and a 'Dead Duck' is one who is absolutely bankrupt past all recovery."
By the early nineteenth century, a lame duck also had the more general meaning of a weak, ineffective, or incapacitated person. It is no doubt this meaning that later transferred to politicians facing the loss of their seats. The Congressional Globe for January 14, 1863 defines "lame ducks" as "broken-down politicians." Several decades later, the New York Evening Post for December 8, 1910 tells readers that "'Lame Duck Alley' . . . is the name [reporters] have given to a screened-off corridor in the White House offices, where statesmen who went down in the recent electoral combat may meet."
When the Constitution was being written, communications were much slower than they are in modern times. In order to allow enough time for all votes to be reported and counted, new administrations did not take office until March. A "lame duck" session of Congress met between the election and the changeover, when legislators who were known to have lost their re-election bids were still creating laws. The so-called Lame Duck Amendment of 1932 corrected this awkwardness, calling for the president and Congress to take office in January instead of March, and eliminating the gap session. Now lame duck usually means people not eligible for re-election.