Washington (CNN) -- Democrats aiming to keep the Senate are facing tough odds in next week's election with their chances depending on convincing a surge of women and African-Americans to vote. Both sets of voters will be vital in two of the crucial races — in North Carolina and Iowa — which new CNN polls show are headed for photo-finishes with only three days of campaigning left. Republicans are especially bullish in Iowa, where their candidate, Iraq war veteran Joni Ernst, leads Bruce Braley by 49% to 47% for a Senate seat Democrats have held for nearly 30 years. Braley leads among women voters by 12 points in the CNN/ORC International survey — but Ernst does three points better than that among men and also dominates the potentially decisive bloc of rural voters.Tuesday's election could determine Senate controlTurnout will be key if Democrats want to maintain their majorityObama appealed to women during a trip to New England
And _ have to watch a few seats of their own. Early voting is especially crucial for the _, because their base voters are historically less prone to show up in midterm elections.