3. Sean Duffy
If Republicans have a good year in 2010, they’ll take out plenty of Democrats in swing seats. If they have a great year, they may defeat senior Democrats such as Rep. Dave Obey (D-Wis.), the 40-year incumbent who runs the Appropriations Committee. Candidate Duffy, who gained celebrity on “The Real World” but has built a real political constituency back in his district, is running explicitly against Obey’s power and influence. A referendum on the Democrats’ economic program — whether voters see it working and worth giving a chance, or whether they want to oust the party for failing — will be in races such as Duffy’s.