Another Democratic Senator has decided to call it quits. Carl Levin of Michigan says he will not run for a 7th term in 2014.

CNN:

Levin, chairman of the Senate Armed Services Committee, called it an "extremely difficult" decision and stated that he'll better serve his Michigan constituents in the next two years of his term by not being distracted by a campaign.

"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," he said in a statement.

During the remainder of his time in Washington, Levin said he plans to focus on his continued push for stricter rules against tax avoidance, saying tax loopholes that allow off-shore accounts are "a major drain on our treasury." He also wants to fight to boost manufacturing and address what he sees as serious flaws in campaign finance laws.

Politico identifies some potential candidates:

A GOP official floated four potential candidates: Rep. Mike Rogers, state Attorney General Bill Schuette, Lt. Gov. Brian Calley and Secretary of State Ruth Johnson.

A Democratic primary is possible. Among those receiving buzz in the wake of the announcement are Rep. Gary Peters and former Rep. Mark Schauer.

Levin, in his sixth term, won with 63 percent in 2008 and 61 percent in 2002. President Barack Obama just carried Michigan with 54 percent in November, despite it being Mitt Romney's home state. Spencer Abraham, in 1994, was the last Republican to win a Senate seat in the state.

Michigan is a fairly blue state and it will take a great candidate running a great race to beat the Democrat. It will be easier in a mid-term election, but will still be an uphill climb given the large presence of unions and traditional Democratic strongholds in the factory towns.