Historically, the party that controls the White House usually loses seats in congressional midterm elections, leading some members to choose not to seek re-election to avoid being ousted by the voters.
But so far this year, the number of announced retirements in both chambers is higher among Republicans, who also must defend more open seats in the Senate than Democrats.
In the Senate, three Democrats, all appointed, have announced they're retiring: Roland Burris is filling out the rest of President Obama's Senate term in Illinois; Ted Kaufman is completing Vice President Biden's term in Delaware; and Paul Kirk was appointed senator from Massachusetts until the late Ted Kennedy's replacement is elected next month.
But six Republicans have announced they're retiring or seeking other offices. All but Sam Brownback -- who's running for governor of Kansas -- are stepping away from politics.
In the House, nine Democrats have announced they are resigning, including six who are seeking other offices. But Rep. Brian Baird, a six-term congressman, caught political analysts by surprise with his announced retirement because the Washington State Democrat held a safe seat.
On the other side of the aisle, 12 Republicans are resigning, including seven who are running for senator or governor.
Back in 2008, six House Democrats retired while 26 Republicans left the House. In 2006, 11 Democrats and 20 Republicans retired rather than seek re-election. The current numbers are consistent.
The nine Democratic and 12 Republican who announced House retirements are quite near the seven Democrats and 13 Republicans that had announced retirements at this point four years ago.