What makes for a good panelist isn't a non-partisan viewpoint; after all, it's often their partisan viewpoint that they're selected for in the first place. Rather, it's the ability to get meta...to talk about the politics behind the politics, as it were, that makes a quality professional kibitzer. It's that ability that makes Rahm Emmanuel and Chris Christie so good on This Week With George Stephanopoulopoulopoulos. (A certain collegiality while trading barbs is nice, too, but not required.)
It's expected for a sitting politician, when interviewed on the talking head shows, to hew to the party line with the unswerving focus of a Gold Squadron pilot in the Death Star trench. That's understood and, while annoying, it's their job.
But the panelists are there to provide informed color commentary, not cheerlead or call plays.
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