Rep. John Tierney is in danger of becoming the first Democrat since 1994 to lose a U.S. House race in Massachusetts. The eight-term incumbent has been dogged by a financial scandal involving his wife and her brothers and an illegal gambling operation. The Republican nominee is Richard Tisei, a former state senator who is openly gay. Tierney has been targeted by more than $3 million in ads this cycle from Tisei, the national Republican Party and pro-Republican groups, eager to defeat a Democrat in Massachusetts. The district is Democratic but the ongoing scandal appears to have taken a toll. A September Boston Globe/University of New Hampshire poll had Tisei with 37%, Tierney with 30% and 30% undecided.

Minnesota 6: Rep. Michele Bachmann (R) vs. Jim Graves (D)

Tea party favorite Michele Bachmann was a shoo-in for re-election when she folded up her presidential campaign in January. Ten months later, Bachmann still has the advantage but she faces a tough challenger in Jim Graves, a wealthy businessman. Graves waged a competitive race in October, spending $1.2 million in TV ads, compared with $1.7 million for Bachmann. The conservative congresswoman has never posted huge numbers on Election Night, but redistricting has made her district slightly more Republican. Defeating a high-profile conservative like Bachmann would be a nice win for Democrats, but she is not at the top of the list of vulnerable Republican incumbents.

Nevada 4: Steven Horsford (D) vs. Danny Tarkanian (R)

New district

There's a competitive race in Nevada's newest congressional district. The nominees are Democrat Steven Horsford, the state senate majority leader, and Republican Danny Tarkanian, a businessman and son of UNLV basketball coaching legend Jerry Tarkanian. The younger Tarkanian was a 2010 U.S. Senate candidate, but placed third in the Republican primary. The two candidates have been evenly matched in terms of fundraising as well as assistance from their national parties and from outside groups in terms of TV ads. The district leans slightly Democratic.

New Hampshire 1: Rep. Frank Guinta (R) vs. Former Rep. Carol Shea-Porter (D)

As was the case in 2010, Republican Frank Guinta and Democrat Carol Shea-Porter face off in the battle for New Hampshire's 1st Congressional District. This time, Guinta is the incumbent and Shea-Porter is the challenger. Shea-Porter was elected in the Democratic wave of 2006 and served two terms before losing to Guinta in 2010, 54%-42%. The two are fairly evenly matched in fundraising.

New Hampshire 2: Rep. Charlie Bass (R) vs. Ann McLane Kuster (D)

Republican incumbent Charlie Bass faces Ann McLane Kuster. Kuster lost to Bass in the general election in 2010 but is running again, and she has outraised Bass, though they started October with roughly the same amount in the bank. The Democrat has far outspent her opponent on the airwaves even though the national Republican Party has invested funds on behalf of Bass. A WMUR/University of New Hampshire poll from early October had Kuster at 38%, Bass 35%, with 25% unsure. The district is more Democratic than the state's other region, which works in Kuster's favor.

New York 24: Rep. Ann Marie Buerkle (R) vs. Former Rep. Dan Maffei (D)

Rep. Ann Marie Buerkle was elected in the Republican wave of 2010 and now has to defend her seat from the man she defeated. Democrat Dan Maffei, a longtime Capitol Hill staffer, won this upstate New York district in 2008 after it had been in Republican hands for almost 30 years. He lost the seat to nurse and tea party favorite Buerkle in one of the closest House races that year. The two have been evenly matched in fundraising and TV ad spending. The district now leans slight more Democratic, which doesn't help Buerkle, who managed to win this seat by only about 600 votes.

North Carolina 7: Rep. Mike McIntyre (D) vs. David Rouzer (R)

Democratic Mike McIntyre is running a competitive race despite a newly redrawn district that skews heavily Republican. The Republican nominee is David Rouzer, a state senator. McIntyre, an eight-term incumbent, leads in fundraising and has kept even with ad spending by pro-Republican outside groups and the national Republican Party. Rouzer has stayed off the airwaves. Like fellow southern Democrat John Barrow in Georgia, McIntyre is showing strong signs of life in a district that appears to have been drawn to end his career.

Ohio 9: Rep. Marcy Kaptur (D) vs. Samuel "Joe the Plumber" Wurzelbacher (R)

Samuel Wurzelbacher, better known as "Joe the Plumber," became a conservative icon in the 2008 presidential race when he challenged then-candidate Obama on tax policy at a campaign event. Republican John McCain even mentioned him during the third presidential debate. Four years later, Wurzelbacher is running for Congress in a quixotic race against 15-term incumbent Democrat Marcy Kaptur, who is a safe bet for re-election. Kaptur handily defeated fellow Democrat Dennis Kucinich in a primary earlier this year.

Ohio 16: Rep. Jim Renacci (R) vs. Rep. Betty Sutton (D)

Ohio's most competitive House race pits freshman Republican incumbent Jim Renacci against three-term Democratic incumbent Betty Sutton. Since August, the two have benefited from about $2 million in ad spending on their behalf from parties and outside groups, while Renacci's campaign has about doubled Sutton's campaign in ad spending. the merged district, located in northeastern Ohio near, but not including, Cleveland, Akron, and Canton, leans Republican but the race remains up for grabs.

Tennessee 4: Rep. Scott DesJarlais (R) vs. Eric Stewart (D)

Republican physician Scott DesJarlais was elected to Congress in the Republican wave of 2010, defeating Democratic Rep. Lincoln Davis. He was a safe bet for re-election until a recent revelation that he had pressured a girlfriend to have an abortion a decade ago. DesJarlais was separated from his wife at the time. The Democratic nominee is Eric Stewart, a state senator. He has begun making an issue of the incident but the impact on DesJarlais' campaign in this rural, conservative district remains unclear.

Texas 23: Rep. Francisco Canseco (R) vs. Pete Gallego (D)

Republican Francisco "Quico" Canseco is one of many freshman members elected in the GOP wave of 2010 who now finds himself in a competitive race for a second term. Canseco was a wealthy commercial real estate developer when he won his third bid for this seat two years ago, defeating Democratic incumbent Ciro Rodriguez. After a legal battle over the redistricting process, Canseco ended up with a district that is slightly more Democratic -- President Obama carried it in 2008 with 51%, according to the Cook Political Report.The Democratic nominee is Pete Gallego, a state representative who defeated former Rep. Rodriguez in the primary. Hispanics make up 66% of voters.

Utah 4: Rep. Jim Matheson (D) vs. Mia Love (R)

As Utah's only Democratic member of Congress, Jim Matheson is used to close races. He barely squeaked by in 2010 with 50% of the vote. This year may prove to be Matheson's toughest race yet. His Republican opponent is Mia Love, the mayor of Saratoga Springs who would become the first female African-American Republican to serve in Congress. Love is a rising star in the party and was giving a prominent speaking role at this year's Republican National Convention. The two have been relatively evenly matched in fundraising. This is one of the most competitive and highest profile House races in the country.

Wisconsin 1: Rep. Paul Ryan (R) vs. Rob Zerban (D)