Political strategist: Clearly, attacking an opposing candidate on philosophical grounds is generally more effective than attacking the details of the opponent’s policy proposals.
Conclusion (clearly)
Attacking an opposing candidate on philosophical grounds in generally more effective than attacking the details of the opponent's policy proposals.
Evidence
A philosophical attack links an opponent's policy proposals to an overarching ideological scheme, thereby telling a story, providing context, and making the attack emotionally compelling.
Evaluate
The conclusion is a comparison between two different strategies, and the author is ultimately trying to say that one strategy is generally more effective than the other.
The stuff we hear about the supposedly better strategy is that it links an opponent's policies to an overarching ideology, thereby telling a story and providing context, and thereby making the attack emotionally compelling.
Since there is a chain of causality or reasoning there, we can suspect that LSAT is testing us on where that chain ends.
Ultimately, we're hearing that attacking on philosophical grounds is more effective because it's emotionally compelling.
Goal
The most likely answer would be a missing link between "emotionally compelling" and "more effective". But the author is also assuming that "linking to an ideological scheme" is connected to being more effective, and that "telling a story and providing context" is connected to being more effective.