Oregon hasn’t voted GOP for President since 1984. As for the last “Conservative” Senator, given that Gordon Smith was to the right of both Bob Packwood and Mark Hatfield, he might be counted. Other than him, you’d likely have to go back to Guy Cordon (1944-55). He narrowly lost to left-wing Democrat Richard Neuberger in 1954 (Hatfield would take the seat back from his widow a dozen years later).
That needs to be taken into consideration before deciding to oppose a potentially appealing Republican running in a liberal constituency. I've backed Tea Party challengers in the past, but I say we should try to cut our losses in this case.