A post-deadline development: Oregon 3rd District Representative Earl Blumenauer has no Republican opponent. That seat is now the only congressional seat in Oregon left open on the ballot by either party.
The reason was the over-enthusiasm of Republican Bruce Broussard. He had, it turns out, filed some months back for a Portland City Council seat, and in Oregon, if you file for two offices at once, you're bounced from the ballot for both. (He might have known, since he falls into the category of "frequent candidate." He also ran for the U.S. Senate in 2004, but failed to snag the Republican nomination.)
The 3rd - which consists mostly of Portland, is overwhelmingly Democratic, and is defended by Democrat Blumenauer - is about as tough for a Republican as the 2nd (eastern Oregon) is for a Democrat. But a range of messages should get out, and doubtless will: A write-in on somebody's behalf at the May primary election seems a probability.