Other Sitting Senators Who Lost Primaries

Numerous news accounts of Joseph Lieberman's primary loss at the hands of Ned Lamont have noted that Lieberman is only the fourth incumbent U.S. Senator to lose in a primary since 1980. Of those four, Shelia Frahm of Kansas had only served for a few months before her defeat, having replaced Robert Dole, who left his seat to devote his time to running for President. New Hampshire Senator Bob Smith lost to the son of a highly connected political family, John Sununu, after having actually briefly leaving the Republican Party a few years before. That two of the other three prior incumbent losses involved somewhat unusual circumstances reveals the oddity of this election.

On the other hand, the 1992 loss of Illinois Democrat Alan Dixon to Carol Moseley Braun is more similar to Lieberman's rejection. Dixon's defeat was widely attributed to his vote in favor of Clarence Thomas' nomination to the Supreme Court.

For a look at these and some other incumbent defeats in primaries going farther back, see here.