BOSTON (AP) -- Massachusetts Sen. Scott Brown is casting himself as an independent Republican voice and Democratic rival Elizabeth Warren says she'll guarantee women equal pay as the nation's costliest Senate contest races toward an Election Day finale. But for all of the cash and careful messaging, the result could hinge on which campaign is better organized to turn out voters.
"I've kept my promise to be an independent voice. I put people ahead of politics and now I need your help to keep that independent tradition alive in Massachusetts," Brown says in his final ad, which features him embracing voters and driving his pickup truck. But it avoids any mention of Brown's party affiliation. While Massachusetts is home to fellow Republican Mitt Romney_whose campaign Brown has endorsed_the only image of a presidential candidate in the 60-second ad is Democrat Barack Obama. The president holds a commanding lead over Romney in the state.
The ad closes: "Vote the person, not the party."
Warren's final pitch, meanwhile, casts her as a fighter for the middle class and portrays Brown as beholden to millionaires, billionaires and "big oil."
"For all the families still struggling, all the people who deserve a decent job, and the women who deserve equal pay. For our kids, crushed by student debt, and our parents, worried about Medicare. Know this: My fight is for you," Warren says in the ad unveiled Wednesday.
They were the closing arguments of a $66 million Senate race, the nation's most expensive in a year of close contests that have left control of the chamber in question. Republicans must gain four seats to win the majority of Obama wins reelection, three if Romney prevails.
With polls showing a tight contest, the result could depend on which candidate has the better-organized turnout operation.
Brown could face stiff headwinds in a state where Republicans hold a small fraction of elected seats, but the state party is mounting what it says is the largest volunteer field operation in its history.
"It is more elaborate, organized and productive than when Scott won the 2010 election because we have had the time to build a robust infrastructure," said party spokesman Tim Buckley.
Warren campaign officials say they're hoping to knock on a million doors and make 2 million phone calls in the final four days before the Nov. 6 election. The Massachusetts Democratic Party and the state's labor unions are also vowing to turn out supporters to help reclaim the seat — held for nearly half a century by Democratic Sen. Edward Kennedy until his 2009 death.
In person and on the air, the candidates are making their closing arguments in a campaign that has put the spotlight on social issues.
Brown and Warren both describe themselves as "pro-choice," but Warren has repeatedly pointed to Brown's support for an amendment that would have let employers and insurers refuse health coverage for services they say violate their moral convictions, including contraception.
Brown said he was defending the religious rights of Catholics, but Warren warned a vote for Brown could help put a conservative majority on the Supreme Court, endangering abortion rights.
Brown has countered by arguing Warren supports higher taxes, including those in the 2010 Affordable Care Act signed by Obama. Brown supports repealing what he calls "Obamacare" and has taken a no new taxes pledge.
There will be no fourth and final debate, a casualty of superstorm Sandy. Warren agreed to a rescheduled debate on Thursday, but Brown declined.