The lone independent member of the U.S. Senate, Jim Jeffords from Vermont, says he will not run for re-election.
At a news conference Wednesday, Mr. Jeffords said he will step down when his term ends next year.
The 70-year-old Senator cited his health and the health of his wife, who is battling cancer, as reasons for his retirement.
Mr. Jeffords won election to the Senate as a Republican in 1988 but he abandoned the party in 2001 because of disagreements with the Bush administration. His defection cost Republicans control of the Senate, which the party had won just a few months earlier.
Republicans regained their majority in the 2002 elections and currently control the Senate by a 55 to 44 margin.