DES MOINES — Theresa Greenfield, the Democratic candidate in Iowa’s U.S. Senate race, has temporarily halted her campaign’s statewide bus tour with less than a week remaining before Election Day after it was revealed that some campaign staffers came into contact with an individual who later tested positive for COVID-19.Greenfield recently tested negative for COVID as part of her regular testing, and is undergoing further tests, the campaign said.Greenfield is challenging Republican first-term incumbent U.S.