Republicans fielded their best possible candidate in former Gov. Linda Lingle, but their hopes of upsetting third-term Rep. Mazie Hirono in this heavily Democratic state are fading.

Lingle, a popular former governor and formidable fundraiser, beat Hirono in the 2002 gubernatorial race, but in a presidential year the state's Democratic tilt and presence of a native son president heading the other party's ticket may be too much to overcome. Regardless of who wins, the state will elect its first female U.S. senator. If Hirono wins, she'll become the first Asian-American woman to serve in the U.S. Senate.

Indiana: Richard Mourdock (R) vs. Rep. Joe Donnelly (D)

Open seat -- Sen. Richard Lugar (R) was defeated in the primary

When six-term Republican Sen. Richard Lugar lost a bitter primary race to state treasurer Richard Mourdock, Democrats gained an unexpected opportunity to take over the seat with three-term Rep. Joe Donnelly.

Though Indiana is a Republican-leaning state, the polls have been close and some longtime Lugar supporters still haven't rallied behind the GOP nominee. Democrats pounded Mourdock for his comment at a debate two weeks before Election Day that "even when life begins in that horrible situation of rape, it is something that God intended." Mourdock the next day clarified his comment and added, "Rape is a horrible thing, and for anyone to twist my words otherwise is absurd and sick."

The full impact of the flap remains to be seen. Donnelly, a relatively conservative Democrat who opposes abortion rights, was one of few red-state Democrats to survive the Republican onslaught of 2010. He has kept the race competitive, but even with the Mourdock comments, Donnelly faces a Republican-friendly electorate and won't get much help from the top of the ticket.

Maine: Charlie Summers (R) vs. Cynthia Dill (D) vs. former Gov. Angus King (I)

Open seat -- Sen. Olympia Snowe (R) is retiring

The unexpected retirement of three-term Sen. Olympia Snowe has set the stage for a three-way contest between Democratic state senator Cynthia Dill, Republican Secretary of State Charlie Summers and former Gov. Angus King, an independent.

King, who quickly rose to frontrunner status, has declined to state until after the election which party he would caucus with in the Senate, though he is widely assumed to align with Democrats. The former governor has endorsements from the Human Rights Campaign, environmental groups and New York Mayor Michael Bloomberg's new super PAC, which supports gay rights, gun restrictions, and education reform.

The national Democratic party has not actively supported Dill but instead has run ads hammering Summers. The national Republicans focused much of their ad fire on King, with the hope that he and Dill will split enough of the anti-Republican vote to ensure a Summers victory. King was at 50% in a poll in mid-September.

Maryland: Sen. Ben Cardin (D) vs. Daniel Bongino (R)

Democrat Ben Cardin should easily beat former Secret Service agent Daniel Bongino for a second term in the U.S. Senate.

Massachusetts: Sen. Scott Brown (R) vs. Elizabeth Warren (D)

Massachusetts is perhaps the one race that has lived up to all its hype and more. As Republican Sen. Scott Brown competes for a full term against Harvard Law School professor Elizabeth Warren, the race for the state's few remaining undecided voters has taken a sharp tone. Brown launched harsh attacks questioning Warren's claims of Native-American heritage while also highlighting his own bipartisanship in the Senate.

Warren continues to attack Brown for protecting millionaires and for vowing to repeal Obamacare while highlighting her advocacy for the middle class and women's issues. Democrats hope the president's popularity and expected wide margin of victory in Romney's home state will counter Brown's popularity to make Warren the first woman to represent Massachusetts in the U.S. Senate.

Michigan: Sen. Debbie Stabenow (D) vs. Former Rep. Peter Hoekstra (R)

Though Democratic Sen. Debbie Stabenow appeared vulnerable at the beginning of the year in her bid for a third term, her fundraising and poll numbers quickly rose while Republicans searched for a candidate.

Winning a four-way primary was former Rep. Pete Hoekstra, who lost a 2010 primary bid for governor. President Barack Obama's popularity, in part due to the auto bailout along with the declining unemployment rate (above the national average, but down about 2 points from January 2009) gives Democrats reason to breathe easier in the Wolverine State.

Minnesota: Sen. Amy Klobuchar (D) vs. Kurt Bills (R)

Democrat Amy Klobuchar is expected to sail to a second term in November. She faces Republican state representative Kurt Bills.

Mississippi: Sen. Roger Wicker (R) vs. Albert N. Gore, Jr. (D)

Republican Roger Wicker should easily win his bid for a full term. He was appointed in 2007 and won a special election in 2008 to finish out the remainder of Trent Lott's term. He faces Democrat Albert N. Gore Jr., who is not a former vice president -- he's an octogenarian retired minister and ex-Green Beret.

Missouri: Sen. Claire McCaskill (D) vs. Rep. Todd Akin (R)