Democrats are already playing hardball with Springfield Mayor Sid Leiken (R), who promises to be the toughest challenger Rep. Peter DeFazio (D) has faced in years.

The Oregon Democratic Party late last week asked state election officials to investigate whether Leiken’s mayoral campaign committee violated state law by paying $2,000 to a polling company that does not appear to exist — but had the same post office box as Leiken’s mother’s real estate company listed on the campaign finance report. The company that received the payment is not registered with state authorities.

The Eugene Register-Guard, which first reported the story, and the Oregonian could not reach Leiken to explain the expenditure. Leiken’s campaign treasurer told the Eugene newspaper that he has records for every expenditure that the campaign made except the one to the polling company.

National Republicans believe Leiken is poised to give DeFazio his toughest challenge in years, and they believe the 4th district seat will be highly competitive if DeFazio chooses to run for governor in 2010.