As for 1988, maybe Oregon was to the left of California and Washington because it's more rural, and Dukakis overperformed in rural America while getting crushed in the suburbs. That's a possibility.
A quick look at the very maps available on this site will confirm otherwise.
Anyway, both OR and WA voted for Dukakis in 1988, so the leftwing trends of Portland and Seattle follow a fairly similar pattern. It's just that Multnomah County makes up a larger percentage of Oregon's vote than King does WA.
