I know fascists do this, but doesn't everyone kind of? If you don't think your enemy has strengths then they're not worth being your enemy and if you don't think they have weaknesses then opposing them is pointless.
edit: I guess one difference is fascists pick enemies that genuinely are powerless, but that doesn't really seem to line up with the original claim
I like this answer, but it makes me think that maybe "the enemy is both strong and weak" could be better phrased as "the enemy is defined in vague and contradictory terms" with the strong/weak doublethink being one example
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