First lady Michelle Obama speaks at a voter registration rally Sept. 8 in Atlanta. (David Goldman/AP)

First lady Michelle Obama will head to Iowa in October to campaign for Rep. Bruce Braley (D) in the hotly contested race for U.S. Senate there, a campaign aide confirmed Wednesday.

Details have yet to be finalized. The news was first reported by the Des Moines Register.

Braley is in a close race against state Sen. Joni Ernst (R), polls show. The campaign has emerged as a key battleground in the fight for the Senate majority. Sen. Tom Harkin (D) is retiring, creating a vacancy.

Campaigning with the first lady may be the best way for Democratic candidates to bring in a big name surrogate without being weighed down by President Obama's public opinion woes. The president's average approval rating in Iowa was a paltry 38 percent during the first half of the year, according to data from Gallup, five percentage points below his national average.

The first lady campaigned for Democrat Michelle Nunn in the Georgia Senate race  Monday.