A coalition of environmental groups is going after Iowa state Sen. Joni ErnstJoni Kay ErnstSenate GOP urges Trump administration to work closely with Congress on NAFTA Overnight Defense: Trump aide's comment mocking McCain sparks outrage | Haspel gets another 'no' vote | Pompeo floats North Korea aid for denuclearization Overnight Energy: Poll finds majority oppose Trump offshore drilling plan | Senators say Trump endorsed ethanol deal | Automaker group wants to keep increasing efficiency standards MORE (R), tying her to former Alaska Gov. Sarah Palin (R) and Charles and David Koch in a new ad.

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The League of Conservation Voters, Sierra Club and Environmental Defense Fund are backing the spot, part of a planned $1 million push to help elect Rep. Bruce Braley (D-Iowa) to the Senate.

The ad features footage of Palin's endorsement of Ernst during the primary, before attacking Ernst for her calls to shut down the Department of Education and abolish the Environmental Protection Agency.

"That's why extremist Sarah Palin and the billionaire Koch brothers want Joni Ernst in Washington," the ad says.

Ernst and Braley are locked in a tight race that will help determine Senate control.