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.

The state has a history of split-ticket voting, giving Heitkamp an opportunity to show her independence from national Democrats. She's publicly disagreed with Barack Obama on issues like energy, which she points to as evidence she won't be a rubber stamp. She enjoys high favorables and solid support from Republican ticket-splitters and has hammered Berg for his connection to a controversial real estate company.

With the lowest unemployment rate in the country, North Dakotans have their choice between two candidates with strong statewide appeal. This race will remain close until Election Day.

Ohio: Sen. Sherrod Brown (D) vs. Josh Mandel (R)

Amid the backdrop of what is arguably the nation's most competitive presidential battleground contest, first-term Senate incumbent Sherrod Brown hopes to prove that the Democratic wave that helped carry him into office in 2006 wasn't a fluke. Brown, who has a voting record the National Journal classified as one of the most liberal in the Senate, made a ripe target for Republicans looking for a pickup opportunity.

But in the home stretch of the 2012 campaign, Ohio remains conspicuously off the list of the most vulnerable Democratic-held seats. The Republican nominee is Josh Mandel, the 35-year-old state treasurer and Marine Corps veteran. Mandel has kept pace with Brown in terms of fundraising, but he continues to trail the incumbent by around 10 points in several independent polls from September and October.

Brown is far from having the race sewn up, especially with the daily volatility at the top of the ticket, but he has a leg up as the race enters its final days.

Pennsylvania: Sen. Bob Casey (D) vs. Tom Smith (R)

Recent polls have given Republicans hope where they previously had little. As Democratic Sen. Bob Casey's lead over Republican businessman Tom Smith began to tighten, the incumbent began actively campaigning across the state -- something he previously hadn't been doing.

Though Republicans have an opening now, Casey still enters the final stretch with the advantage. The state has not emerged as a contested presidential battleground and a strong showing by Barack Obama here could help Casey beat back this unexpected and late-breaking challenge.

Rhode Island: Sen. Sheldon Whitehouse (D) vs. Barry Hinckley (R)

Democrat Sheldon Whitehouse is a safe bet to win a second term in November. He faces Republican businessman Barry Hinckley.

Tennessee: Sen. Bob Corker (R) vs. Mark Clayton (D)

Unlike the tough battle he had in 2006 to take the seat, Republican Bob Corker should easily win a second term in November. He faces Democrat Mark Clayton, whose candidacy has been disavowed by the Tennessee Democratic Party for his involvement with an anti-gay rights group.

Texas: Ted Cruz (R) vs. Paul Sadler (D)

Open seat -- Sen. Kay Bailey Hutchison (R) is retiring

After a tough primary victory over the candidate endorsed by Gov. Rick Perry and the state party establishment, Republican nominee Ted Cruz, the former state solicitor general, is now heavily favored this November in his race against Democratic nominee Paul Sadler, a former state representative.

Utah: Sen. Orrin Hatch (R) vs. Scott Howell (D)

Republican Orrin Hatch learned an important lesson from his former colleague Sen. Bob Bennett in 2010 -- don't take the Republican nomination for granted. Hatch campaigned early and hard to win the GOP nomination over tea party favorite Dan Liljenquist, a former state senator. Hatch now is the overwhelming favorite to win a seventh term in November.

A Democrat hasn't represented Utah in the U.S. Senate in 36 years.

Vermont: Sen. Bernie Sanders (I) vs. John MacGovern (R)