Why is Case seen as less electable? Doesn't that go against the notion of more moderate = more votes?
That isn't necessarily true, especially since Hawaii is not a swing state. For Hawaii Democrats, base turnout is probably more important than courting independents. Hirono is well-respected for her work as Congresswoman, liked by the liberal base and supported by key elements of the Democratic power structure both in Hawaii and nationally. Case is seen by many Democrats as a sellout due to his run against Akaka in 2006 and various apostasies on the issues (voting against Planned Parenthood funding, etc.).