The Larsen Analysis in Whatcom County

The Washington Post is running a fascinating article on the election results, with a chart that maps the endorsements of candidates from "Freedom Works", "Tea Party Express", Sarah Palin and the confluence between these groups.  The 2nd Congressional was one of the six races where all three of these groups were apparently endorsing the same candidate (John Koster).  Despite this, Larsen narrowly won his seat, after winning his three previous elections by over 60%. 
Why were San Juan and Whatcom County so resistant to the combined right wing push against Larsen? Below is what the final total will probably look like, excluding the 260 total votes from the small corner of King County that is part of second congressional. Essentially, Larsen drew even in Island and Skagit counties, San Juan (the most progressive vote in WA State), nullified his narrow loss in Snohomish (the most populous county in the 2nd Congressional), and Whatcom County assured most of his margin of victory. Since the vote drifted left as the counting continued (at least it did so in Whatcom County), we can assume Larsen benefited from high turn out.