Via a Politico news alert:
Sen. Carl Levin (D-Mich.) announced Thursday he will not seek reelection in 2014. The six-term, 78-year-old senator wrote in a statement that he and his wife "struggled" with whether to retire but decided he could better focus on issues such as reforming the Tax Code and boosting manufacturing over the the next two years "without the distraction of campaigning for reelection."
For more information... http://www.politico.com
Levin is the chairman of the Senate Armed Services Committee.
UPDATE: Here is is statement, in part. More at CNN:
I have decided not to run for re-election in 2014.
This decision was extremely difficult because I love representing the people of Michigan in the U.S. Senate and fighting for the things that I believe are important to them.
As Barbara and I struggled with the question of whether I should run again, we focused on our belief that our country is at a crossroads that will determine our economic health and security for decades to come. We decided that I can best serve my state and nation by concentrating in the next two years on the challenging issues before us that I am in a position to help address; in other words, by doing my job without the distraction of campaigning for re-election. [...]
A third item I want to tackle is a growing blight on our political system that I believe I can help address: the use of secret money to fund political campaigns.