Michigan Democratic Sen. Carl Levin's decision not to run for reelection in 2014 opens the door slightly for Republicans in a race that Democrats would have been heavily favored to win had Levin run for reelection.

That said, it's not yet obvious who will run -- on either side. In fact, for a such a populous state, the GOP and Democratic statewide benches are relatively thin in Michigan.

Let's start with the Democratic side. The most obvious possibility is Rep. Gary Peters, who represents a Detroit-area district. Peters stands out in the Democratic congressional delegation, which is populated mainly by older members who have been in the House for decades. Democratic Reps. Sander Levin (Sen. Carl Levin's brother), John Dingell, and, and John Conyers are all in their 80s.

Peters might also have an eye on the governor's race. Republican Gov. Rick Snyder is looking vulnerable, and with Democrats yet to coalesce around a Snyder opponent, Peters might look in that direction.

Another name to keep an eye on is former Democratic governor Jennifer Granholm, whose name ID would make her a candidate to watch from the get-go. But Granholm left office is less-than-ideal political shape, which is something that must be taken under consideration, too.

One more Democratic name worth watching is Debbie Dingell, the wife of Congressman Dingell.

On the Republican side, Attorney General Bill Schuette is a name that Republicans are already pointing at. Schuette used to be a member of Congress. Lt. Gov. Brian Calley is also a possibility and so is Secretary of State Ruth Johnson. And Clark Durant, who ran as a conservative outsider in 2012 Senate race, might be tempted to give another run a close look.

From the House delegation, Rep. Mike Rogers (R) is a possibility, but if he were to run, he'd be giving up a plum posting as chair of the House Intelligence Committee. Rep. Candice Miller is another GOP option. And Rep. Justin Amash, a libertarian-leaning Republican who has been at odds with Republican leadership in the House, is also a name to keep tabs on. If Amash runs, he could present headaches for establishment Republicans.

As a whole, Michigan leans Democratic, which gives the party a good chance of holding onto the seat, even without Levin in the picture. President Obama carried the state by nine points in 2012 and 16 points in 2008. But 2014 will have no presidential race at the top of the ticket. And as Michigan Republicans showed during the 2010 midterm GOP wave, they can win statewide under the right conditions.

Levin is the seventh senator to retire or resign this cycle. Sens. Saxby Chambliss (R-Ga.), Frank Lautenberg (D-N.J.), Mike Johanns (R-Neb.), Tom Harkin (D-Iowa) and Jay Rockefeller (D-W.Va.) are all retiring at the end of their current terms. Republican Jim DeMint of South Carolina resigned earlier this year to head the conservative think tank the Heritage Foundation.