Carl Levin is retiring. (Melina Mara/Washington Post)

Sen. Carl Levin (D-Mich.) will not seek reelection in 2014, he announced Thursday afternoon, saying he wanted to focus on the nation's challenges rather than politics.

In a statement, Levin explains that he and his wife "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."

The 78-year-old senator has held his seat since 1979; he is chairman of the powerful Armed Services Committee. He has not faced a close election in decades.