http://www.surveyusa.com/client/PollReport.aspx?g=254081ec-e21b-4a73-91f3-a6cc8e4ba75dWashington is a swing state. While it has voted Democratic recently, it is a state Democrats can't take for granted. In fact, it's probably a more vulnerable state than New Jersey or Massachusetts for the Democrats. If we don't carry Washington, we WON'T win this election. Whereas, Democrats can still realistically lose Ohio or West Virginia and still pull it out.
So while Clinton can claim the Big State argument, it doesn't hold much water when you realize nominating her could flip Washington and possibly Oregon.