Sen. Carl Levin, D-Mich., chairman of the Armed Services Committee, announced Thursday afternoon that he will not seek re-election in 2014.

Levin, who is 78, was first elected to the Senate in 1978 and is the longest-serving senator in Michigan's history.

Levin's retirement creates an open seat for Democrats to defend, but Republicans have not won a presidential or senatorial vote in Michigan in decades.

In his statement, Levin said: “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. …  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.”

Among those issues, he cited cracking down on corporate tax dodges, fostering Michigan’s “manufacturing renaissance” and fighting “the use of secret money to fund political campaigns.”