Well, as a work of propaganda you may want to start by looking at how others have done it, the context in which the cartoon was produced and the audience to which it was addressed, and then continue on by looking at other propaganda cartoons of the period in comparison. You might break down the individual elements of the cartoon, the visual rhetoric involved and how that reflects a given point of view at a given time. If it is possible to identify the artist, it might be interesting to see where they were in their life & career at the time when the cartoon was made - whether it reflects a continuation of themes or a break into new ground.

I would strongly recommend Scully & Quartly's Drawing The Line: Using Cartoons As Historical Evidence as a starting point, as well as Schroeder's Red Scare Propaganda in the United States: A Visual and Rhetorical Analysis which might help you come to grips with the topic.

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