Not necessary, becauase what people are likely to “remember” has no bearing on the logic of the argument. We know that philosophical attacks are more emotionally compelling because they tell a story and provide context. The author doesn’t have to think that people’s likelihood of “remembering” the story/context has anything to do with what makes the attack more compelling.

Necessary, because if it were not true — if political attacks that are emotionally compelling are NOT generally more effective than those that are not — then we have no reason to think that philosophical attacks are more effective on the basis of their being emotionally compelling. The premise about being emotionally compelling would provide no support to the conclusion if (B) were not true. So the author must assume that (B) is true.

Not necessary, because the author never assumes a causal relationship between “story” and “context.” We know that philosophical attacks both tell a story and provide context, but we don’t know if attacks that tell stories are in general able to provide more context than those that don’t.

Not necessary, because the author’s reasoning doesn’t rely on any claims about what people are “interested” in. The reasoning is based on philosophical attacks being more emotionally compelling than attacks on details of proposals. Whether people are interested in details has no bearing on whether attacks on details are more emotionally compelling or on the relationship between being emotionally compelling and effectiveness.

Not necessary, because whatever is true about most candidates’ policy proposals has no effect on whether a philosophical attack can link a proposal to an ideology. Maybe most proposals are not grounded in ideology; they can still be linked to an ideology through a philosophical attack.