Rep. David Wu (D-Ore.) was already facing a tough primary when allegations that he had an "unwanted sexual encounter" with the teenage daughter of a supporter surfaced on Sunday.

He announced he would not seek reelection but thus far has refused to resign from his seat. Either way, with Wu out of the picture, Democrats should have no trouble hanging on to the seat.

Oregon Labor Commissioner Brad Avakian (D) and state Rep. Brad Witt (D) had already begun to campaign against Wu. Avakian blasted him for refusing to resign, saying Wu could no longer be an effective House member and that ensuing investigation by the House Ethics Committee would create unnecessary trauma for the girl Wu allegedly pursued.

"David Wu's reported plan to remain in office but not seek reelection puts David Wu first and his constituents last," Avakian said in a statement. "An ethics investigation would result in a long, drawn out distraction and prolong the public pain of this young woman and her family."

The district gave President Obama 61 percent of its vote in 2008, and while it became a few points more Republican because of redistricting, it is unlikely that Republicans can contest the seat. 

Republican sources familiar with the district said that they are unlikely to seriously contest the race. Even with mounting reports of erratic behavior in a strong year for the GOP, Wu still won reelection with 55 percent of the vote last fall.

Should Wu change his mind and resign, Democratic Gov. John Kitzhaber would set a date for a special election. Depending on when that election is called, the parties would either nominate candidates internally by party rule, or there will be a special primary election and candidates would file for that.