4 Democratic Senate races to watch - They are MUST WIN seats if the Democrats have any hope to regaining the Senate majority. OH- former Gov. Ted Strickland (D) will challenge Sen. Rob Portman (R). IL - Rep. Tammy Duckworth (D) will challenge Sen. Mark Kirk (R). WI - former Sen. Russ Feingold (D) will challenge Sen. Ron Johnson (R). CO- former St. AG Catherine Cortez Masto (D) will run for the Harry Reid seat (National Journal).