Special election to fill the remainder of the term of Harry Lane, who died May 23, 1917.
Charles McNary, the appointee who replaced Lane in 1917, did not run in the special election, opting instead to run for the full term beginning March 4, 1919. Mulkey duly replaced McNary on November 6, 1918, but resigned on December 17, 1918. McNary was reappointed to serve the remainder of the term.
Source for Popular Vote data: Oregon Secretary of State. Blue Book and Official Directory 1919-1920, Oregon Secretary of State (https://babel.hathitrust.org/cgi/pt?id=inu.30000091790844&view=page&seq=158) (accessed 15 Sep 2023)