What stunned me was that not a single Slater expressed so much as a soupcon of support for, much less an intention to vote for, the other "liberal" candidates on the ballot. And this despite the fact that most of these writers live in solidly Democratic states where there is no reasonable fear of "spoiling."

Looks a lot more like Dem hackdom to me than "liberal bias."

Perhaps it is a "liberal bias" without being a "loony bias". A vote for a third party candidate is only good for earning radical cred, and no-one who spends that much time around politics should even consider throwing away their vote.