Michigan Democrat Sen. Gary Peters announced Tuesday that will not seek reelection next year.

His departure is expected to result in a highly contested race for the Senate seat in the battleground state.

The 66-year-old Peters is unexpectedly retiring after just two terms. 

He led the Democratic Senatorial Campaign Committee through a successful 2022 election cycle in which his party won  a number of hotly contested races to keep control of the upper chamber. But two years later, Republicans flipped several highly competitive seats, costing Democrats their Senate majority, according to the Associated Press.