Republican Sen. Joni Ernst is trailing her Democratic challenger for Iowa's Senate seat, putting a once-safe GOP race in doubt, according to an early poll.Ernst, 49, has support from 43% of likely Iowa voters compared to 46% who told Des Moines Register/Mediacom Iowa Poll researchers they'd cast a ballot for Democrat Theresa Greenfield. Another 7% remain undecided.J. Ann Selzer, whose firm Selzer & Co. conducted the poll, said this was the first survey fielded since Ernst, a President Trump ally, first ran for the Senate in 2014, which showed her behind her opponent.“Symbolically, that's certainly meaningful, even if Theresa...