Plagued by scandals and a conservative electorate, Democrat Claire McCaskill seemed likely to become a one-term senator. That was until her opponent, six-term Republican Rep. Todd Akin, said in a local news interview that women have biological ways to avoid pregnancy after a "legitimate rape."
With a second wind to her campaign, McCaskill pounced as her poll numbers rose and Akin's dropped. Akin refused to drop out of the race despite requests from the GOP establishment. Some conservatives, including Jim DeMint, Newt Gingrich and Rick Santorum, rallied behind him. Other Republicans kept their distance, though some have come back around out of strong desire to unseat McCaskill.
With a lead over Akin, McCaskill sought to solidify her candidacy for a second term by running ads with female Republican rape survivors planning to vote for her because of Akin's comments. Missouri is still a competitive state for any Democrat, but unless local Republicans come back to Akin in droves, McCaskill appears headed to win a second term.
Montana: Sen. Jon Tester (D) vs. Rep. Dennis Rehberg (R)
Democrat Jon Tester knew he'd have an uphill battle to a second term against six-term Rep. Denny Rehberg. Both are known quantities with high favorables in the state, though neither has been able to crack 50% in the polls. Both campaigns have gone negative in the fight over Social Security, and both say the other is distorting their views.
Like the Massachusetts race, there are few undecideds left, except here Republicans are hoping that works in their favor. Though the state has a history of voting for Democrats statewide along with a Republican for president, Barack Obama's disapproval ratings could drive the strong GOP turnout Rehberg needs to move up a chamber in Congress.
Nebraska: Former Sen. Bob Kerrey (D) vs. Deb Fischer (R)
Open seat -- Sen. Ben Nelson (D) is retiring
Republicans began eyeing two-term Democrat Ben Nelson's seat even before he announced his retirement. With Nelson out, Democrats pinned their hopes on Bob Kerrey, the former governor and two-term senator. Although a well-known figure in Nebraska, Kerrey spent most of his post-Senate career outside of the state, primarily in New York City where he served as president of The New School.
The conservative super PAC American Crossroads began running ads against Kerrey before he even declared his candidacy. The Republican nominee is state Rep. Deb Fischer, who scored a surprising win in a crowded GOP primary. Kerrey has an uphill battle to keep the seat blue; Fischer has been leading with at least 50% in both independent and partisan polls.
Nevada: Sen. Dean Heller (R) vs. Rep. Shelley Berkley (D)
Democrats' strength in Nevada is being put to the test once again in a Senate election. With voter registration numbers on their side, seven-term Democratic Rep. Shelley Berkley hopes to deny Republican Sen. Dean Heller a full Senate term (Heller was appointed to the seat after Republican John Ensign resigned).
A House ethics investigation and a lackluster debate performance have kept Berkley below Heller in the most recent polls. Heller's strong fundraising ability also helped him keep the advantage in a state with a heavy Latino population that overwhelmingly votes Democratic. Both parties are hoping for a win here, though the race should remain close through Election Day. Turnout for the presidential race could have the largest impact on the outcome of this race.
New Jersey: Sen. Robert Menendez (D) vs. Joe Kyrillos (R)
Democrat Bob Menendez is expected to win a second term easily. He faces Republican state Sen. Joe Kyrillos.
New Mexico: Rep. Martin Heinrich (D) vs. former Rep. Heather Wilson (R)
Open seat -- Sen. Jeff Bingaman (D) is retiring
Republicans were initially hopeful that Democratic incumbent Jeff Bingaman's decision to retire presented a pickup opportunity. Their nominee, former Rep. Heather Wilson, has a reputation for being a moderate in this increasingly Democratic-leaning state, but she lost a bruising Senate primary four years ago and has had difficulty getting her footing against Democratic nominee Martin Heinrich, a two-term congressman.
The two have been evenly matched in both fundraising and candidate-sponsored TV ads. However, according to ad spending data from the Campaign Media Analysis Group, the Democratic party and outside groups began pulling their ads in this race three months ago and most Republican groups have since followed suit, a sign that race was becoming less competitive. Both independent and partisan polling since the summer has shown Wilson stuck in the low 40s, with Heinrich leading by various margins.
Wilson also cannot rely on a competitive presidential race at the top of the ticket to help boost turnout in her favor. Heinrich enters the final stretch with a clear advantage.
New York: Sen. Kirsten Gillibrand (D) vs. Wendy Long (R)
Democrat Kirsten Gillibrand should easily win her first full term to the Senate. She faces attorney Wendy Long, a former clerk to Supreme Court Justice Clarence Thomas.
North Dakota: Heidi Heitkamp (D) vs. Rep. Rick Berg (R)
Open seat -- Sen. Kent Conrad (D) is retiring
Former state Attorney General Heidi Heitkamp gives Democrats their best opportunity to keep the seat of retiring five-term Sen. Kent Conrad. Republicans hope first-term Rep. Rick Berg will repeat the party's success of 2010, when they took over retiring Democrat Byron Dorgan's seat.