Gary Peters' exit creates a highly contested U.S. Senate battleground seat expected to be coveted by both major political parties.

Michigan Gov. Gretchen Whitmer said she will not run for the open U.S. Senate that will be vacated by retiring Sen. Gary Peters.

Pete Buttigieg, 43, a former presidential candidate who's viewed as a rising star by many in Democratic politics, had been floated as a potential candidate for governor next year.