(TNND) — The fierce battle for the Senate may come down to who wins in Maine in a race that is shaping up to be one of the most expensive in U.S. history as Republicans and Democrats prepare to pour tens of millions into boosting their candidates.Winning Maine’s Senate seat is key to both parties’ chances of holding a majority at the end of the midterm elections, which has put an intense spotlight on the race between Democratic nominee Graham Platner and Republican Sen. Susan Collins. Democrats need to flip four seats to retake control of the Senate and view...