She was the Democratic nominee for the 2020 United States Senate election in Iowa, losing to incumbent Republican Joni Ernst.

[6] She helped with farm jobs such as driving tractors and grain trucks, bailing hay, and feeding hogs; and by the age of 16, assisted in negotiating contract terms and demarcating fields for the family crop-dusting business.

[12] In 2012, she became president of the Des Moines commercial real estate firm Colby Interests,[13] based in Windsor Heights, Iowa.

She is a member of the board of the American Institute of Certified Planners, Commercial Real Estate Women of Iowa, and the Windsor Heights Chamber of Commerce.

[21][22] On June 2, 2020, she won the Democratic primary with 47.71% of the vote, defeating three other major candidates, including Michael T. Franken, a retired U.S. Navy admiral and former aide to U.S.

[35] Greenfield received endorsements from former president Barack Obama,[36] Minnesota Senator Amy Klobuchar,[37] Massachusetts Senator Elizabeth Warren, Representative Abby Finkenauer,[38] Representative Dave Loebsack,[38] former Iowa first lady and education advocate Christie Vilsack, and former lieutenant governor of Iowa Sally Pederson.

[45] In 2021, President Joe Biden appointed Greenfield as Iowa director for the U.S. Department of Agriculture's Rural Development program.

[48] She proposed a ban on corporate Political Action Committee money, passing lobbying reforms, and overturning the Supreme Court's decision on Citizens United.

She criticized Senator Joni Ernst for taking money from the oil industry and for denying the scientific consensus on climate change.

[54] In 1985, Greenfield married Rodney Wirtjes, an electrician, who served as a journeyman lineworker and a member of the International Brotherhood of Electrical Workers.