Final answer:
Nash's credibility is affirmed through his education, professional background, and evident research on the subject. Credibility is also based on the expert's testimony aligning with broader consensus and absence of bias. Verification from credible sources, such as Lewis's documents in the Library of Congress, further supports this credibility.
Step-by-step explanation:
To assess whether Nash is a credible authority on the topic, it is important to consider not just his self-referential statements but also his education, professional background, and community involvement. Nash's credibility is bolstered by a history of researching the subject at hand, as well as his lack of obvious bias. In understanding credibility, an expert's testimony must reflect both a deep understanding of the subject and alignment with the consensus among other experts. Having an agenda or a history of disseminating misinformation would understandably diminish the author's trustworthiness.
Additionally, Hayden notes that documents relevant to Lewis's political efforts are housed at the Library of Congress, which is a pertinent detail highlighted to ensure the readers about the credibility and so that readers can verify the information if needed. Moreover, evaluating various sources and considering potential biases or omissions is important in the larger analysis. When looking at the detail about the famous debate between John F. Kennedy and Richard Nixon, the perception of credibility based on non-verbal cues, such as Nixon's sweating, suggests that credibility also takes into account the manner of presentation, not just content expertise.
Ultimately, determining credibility requires a combination of the individual's expertise, consensus with other experts, track record, absence of bias, and alignment with credible evidence. Thus, Nash's credentials combined with proper backing by credible evidence and a consensus among experts in the field would make his authority on the topic more persuasive to the audience.