6 p.m. Update: Dems fight for Senate control

WASHINGTON (AP) - Majority Democrats fought Republicans for control of the Senate on Tuesday after a bitter campaign marked by roughly $1 billion in outside spending in competitive races from Virginia to Montana.

Republican Sen. Scott Brown, who stunned Democrats in January 2010 by capturing Sen. Edward M. Kennedy's Massachusetts seat, was the underdog against Democrat Elizabeth Warren in one of the nation's costliest races. The two candidates agreed to no outside money by super PACs and other independent groups then together spent $68 million on their campaign.

Democrats currently hold 51 seats in the Senate plus two independents who caucus with the party. Republicans have 47 seats and a loss early on in Massachusetts would make their path to the majority even harder.

Republicans need a net of four seats, three if Republican Mitt Romney wins the presidency.

The arithmetic was daunting for Democrats at the start of the election cycle - they had to defend 23 seats to the GOP's 10. Further complicating the calculation were Democratic retirements in Virginia, Wisconsin, North Dakota, Hawaii, Nebraska and New Mexico as well as the retirement of independent Connecticut Sen. Joe Lieberman, the Democratic vice presidential nominee in 2000.

Republicans faced retirements in Arizona, Texas and Maine, the latter a shock to the GOP as Sen. Olympia Snowe expressed frustration with the Capitol's partisan gridlock and decided to leave Washington.

Republican hopes of reclaiming the Senate suffered a major blow when GOP candidates in Missouri and Indiana made awkward remarks about rape and abortion.

In Missouri, Democratic Sen. Claire McCaskill was considered the most vulnerable incumbent, but Republican Rep. Todd Akin severely damaged his candidacy in August when he said women's bodies have ways of avoiding pregnancy in "legitimate rape." GOP leaders, including Romney, called on him to abandon the race. Akin stayed in and is counting on support from evangelicals to lift his prospects in a state that favors Romney.

In Indiana, tea party-backed state treasurer Richard Mourdock was considered the favorite after knocking out six-term Sen. Richard Lugar in the GOP primary in May.

But he damaged his chances when he said in a debate that pregnancy resulting from rape is "something God intended." Moderate Democratic Rep. Joe Donnelly held a slight lead in polling heading into the election. Libertarian Andrew Horning's presence on the ballot could affect the outcome.

Democrats and Republicans in a dozen states faced an onslaught of outside money that financed endless negative commercials and ugly mailings that left voters exasperated. The record independent spending - $50 million in Virginia, $40 million in Wisconsin and $33 million in Ohio - reflected the high-stakes fight for the Senate.

In the closing days of the campaign, polls showed a tightening race in Ohio where Democratic Sen. Sherrod Brown faced a challenge from state treasurer Josh Mandel and in Pennsylvania where Democratic Sen. Bob Casey tried to fend off businessman Tom Smith, who invested more than $17 million of his own money.

Maine provided the most intrigue with independent Angus King the front-runner against Republican Charlie Summers and Democrat Cynthia Dill.

King has not said whether he would caucus with Democrats or Republicans and the outcome of the presidential election is certain to have a bearing on any decision. However, the expectation has been that he would side with the Democrats after Republicans such as Karl Rove's group and the U.S. Chamber of Commerce spent hundreds of thousands of dollars criticizing him.