Paul Diller, the Democratic nominee in Senate District 13 has abandoned his challenge to incumbent state Sen. Kim Thatcher (R-Keizer).

Diller is a professor at the Willamette University College of Law and a first-time candidate. Although SD 13, which covers parts of Clackamas, Marion, Washington and Yamhill Counties, has been reliably Republican in the past, voter registration has shifted since 2014, when Thatcher won her seat.

In 2014, registered Republicans outnumbered Democrats by 4,568. Today, that Republican advantage has narrowed to just 1,653. Democrat Hillary Clinton won the district in 2016.

Senate Democrats, like their colleagues in the House, are just shy of the three-fifths super-majority needed to pass tax measures. They currently hold a 17 to 13 advantage and need to pick up just one seat in November to get a super-majority.

Diller would certainly have had a difficult task in defeating Thatcher, who served five terms in the House before moving up to the Senate in 2014 but now Democrats will have to identify a new candidate and start from scratch.

"I am sad to announce that I am withdrawing my candidacy as the Democratic nominee for Senate District 13," Dillard said in a statement. "The stresses of campaigning have begun exacting a significant toll on me and my family, particularly with two young sons. I cannot in good faith continue this campaign through November while balancing family responsibilities."

Tom Powers, a spokesman for the Senate Democratic campaign committee, says the Democratic Party of Oregon will soon meet to select a replacement for Diller.