Former Michigan governor Jennifer Granholm (D) will not run for retiring Democratic Sen. Carl Levin's seat, she announced Friday.

"Friends, thanks for all of the encouragement on the Michigan Senate seat, but I'm not going to run," Granholm wrote on her Facebook page. "I appreciate all of the outreach I've received; for several reasons it's just not right for us (it's a family decision). My best to all the contenders -- Levin's US Senate seat will stay blue!"

Granholm served two terms as Michigan's governor, and was pretty unpopular when she left office in 2011.

Levin announced his retirement plans earlier this month. The Republican and Democratic fields in the race to replace him have yet to take shape. On the Democratic side, Rep. Gary Peters is viewed as a top potential recruit. Debbie Dingell, the wife of Rep. John Dingell (D), is another Democrat to watch.

On the Republican side, Rep. Mike Rogers, the chairman of the House Intelligence Committee has been mentioned as a possible candidate. So has Rep. Justin Amash, a libertarian-leaning Republican who has clashed with House GOP leadership.

The last time Michigan voters elected a Republican senator was 1994.