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
Clara Zetkin's The Struggle Against Fascism is my answer on this. Because fascism is a coming together of several groups with conflicting interests, all fascism can offer is a sham revolution, and by extension a sham enemy. It's up to the subject and their class to decide what the enemy is specifically. Like a rorschach test. But under this subjectivity, they are united as one universal movement.
The role of a fascist in history is to unite proletarians, with petite bourgious and with the bourgious. There's no way of doing this without animating an imaginary enemy that all members of the piggish masses can agree with.
A fascist leader can do with this vague enemy whatever they wish. If they want to do something which a majority of their masses will be against, a leader can say the imaginary enemy has won the battle, but not the war. If they succeed in something, the leader can get their masses drunk off their imaginary victory.
This is Trump's entire administration imo.
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
deleted by creator
:this:
Zetkin also highlights that fascism will be somewhat weak/vulnearable as it starts to take power and becomes inevitably beauracratised. As its a sham revolution, it will never be able to provide the degree of strength, prosperity and security that it promised its followers.
Thus its appropriation of anti-capitalist rhetoric is revealed as demagogy instead of a real, material, political program for the working class. Contradictions re-emerge and the sections of the working class that supported it turn against it, giving socialists a chance to agitate and fight back against it.