In 1994, a lot of Democrats -- 20 of them -- retired rather than run for their seats. In 2008, 28 Republican representatives retired rather than face another Democratic onslaught. Today, news comes that Rep. Dennis Moore, a conservative Democrat from Kansas is retiring rather than run for his seat; he is the only Democrat in the House to retire for reasons other than running for higher office. But if it becomes a trend, Dems should worry.
Currently, no Republicans are leaving their seats except to run for higher office; in total, 12 Republicans and seven Democrats are leaving their seats open for various reasons. Right now, those numbers don't predict much about next year's elections, but it's still early yet; typically, members of Congress announce their decisions to retire or run in winter or spring of the election year, giving their respective parties time for a proper primary campaign. Watching the relative number of Democrats versus Republicans who leave behind open seats is one way to gauge what will happen eight months later and the general mood among the two parties going into the midterms.
-- Tim Fernholz