Passage Summary: Some think great leaders either lead the public or follow it, but the author points out that successful legislative leaders actually do both at the same time.

Conclusion: It is incorrect to view the 'shaping public opinion' and 'reacting to public opinion' hypotheses as mutually exclusive.

Reasoning: Every leader who has successfully passed legislation has demonstrated skill in both shaping and reacting to public opinion.

Analysis: There is a subtle 'scope shift' here that you need to catch. The first sentence talks about 'great national leaders,' but the evidence talks about 'leaders successful in passing programs.' For the argument to hold, the author must assume that these successful legislative leaders are representative of 'great national leaders.' If a leader could be 'great' without passing programs (and thus perhaps only doing one of the two things), the conclusion wouldn't necessarily follow. Look for an assumption that links legislative success to the definition of a great leader.