Washington (CNN) - Though all 435 seats in the U.S. House of Representatives will be up this November, the battle to control the chamber next year will come down to a much smaller number of congressional districts scattered across the country. CNN has identified the top 100 House races, which we've dubbed "The CNN 100," and will profile one of these races at random each day for the next 100 days until the election. These seats run the gamut both politically and demographically: red states and blue states, urban and rural, open seats and seats with incumbents facing their first competitive race in years. Some are highly competitive, while the race is still developing in others. Today's featured district is:
Wisconsin 7th (Open seat) – Rep. David Obey (D) is retiring
Primary: September 14, 2010
Location: Northwestern Wisconsin
Days until Election Day: 100
Although incumbent Democratic Rep. David Obey's decision not to seek a 21st full term in Congress gives Republicans a better shot at picking up this seat in November, the 41-year House veteran likely would have faced his most competitive race in years had he decided to stay in.
Leading the Republican charge is Sean Duffy, a former Ashland County district attorney with national television exposure both from his stints as a professional lumberjack athlete and commentator on ESPN and as a cast member on the long-running MTV reality programs "The Real World" and "Road Rules."
Duffy launched his House bid before Obey had decided to retire and focused much of his campaign portraying the incumbent as a top-spending Washington insider. By the end of March, Duffy proved he was a credible candidate, at least in terms of fundraising, having raised $506,000, which was more than five times the amount the 2008 GOP nominee, Dan Mielke, raised for his entire 2008 bid against Obey. Mielke is running again this year but had only $1,500 in the bank at the end of June. Duffy had banked $664,000 as of June 30 and had raised $971,000.
The likely Democratic nominee is Julie Lassa, a state senator and daughter of Wisconsin dairy farmers. Lassa was elected to her state senate seat in 2003, after serving four years in the state Assembly. She had $304,000 in the bank as of the end of June, which is less than half of Duffy's amount, though Lassa has only been a candidate since mid-May, when Obey announced his retirement. She faces only nominal opposition for the Democratic nomination. Like Duffy, Lassa had not been born when Obey took his House seat in April 1969.
Geographically, Wisconsin's 7th district is huge. It comprises the entire northwest quarter of the state and occupies more square mileage than the states of Delaware, Maryland, and Rhode Island combined. Obama carried the district with 56 percent in 2008, but President Bush almost won here in 2004, with 49 percent of the vote compared to 50 percent for John Kerry.
The race would have worth monitoring had Obey run for re-election; now that he's out, it will be very competitive.