DES MOINES, Iowa Four relatively unknown Iowa Democrats are competing in a primary Tuesday to take on Republican Sen. Joni Ernst, an endeavor viewed as a long shot when better-known prospects last year took a pass on running. But as Democrats are increasingly bullish about their prospects in places such as Arizona and Colorado, the Iowa race is getting renewed attention as a potential battleground that could help the party regain the Senate majority. Greenfield's fundraising prowess reflects a broad array of support among Iowa Democrats. As of a week ago, nearly 500,000 Iowa voters, about one-quarter of the states electorate, had requested absentee ballots, the highest number of absentee ballot requests for any Iowa election, primary or general. The influx of primary-voting Democrats, including those who have been less active in recent cycles, could signal a resurgence of Iowa Democrats.