Final answer:
The excerpts from the text emphasize Barack Obama's race during the 2008 election, making it the characteristic that stands out across multiple mentions, including the historical significance of his candidacy as the first African American president.
Step-by-step explanation:
The excerpts highlight various aspects of Barack Obama's characteristics during the 2008 election, but the one that stands out for the multiple mentions across the excerpts is his race. While the excerpts touch upon his experience, optimism, and education, his race is discussed in the context of the historical significance of his candidacy and the various reactions it provoked within the electorate. For instance, the text notes Obama as 'the first African American president' and discusses the role of race in the election and the voters' response to it. Therefore, the answer is A. his race.