Whatever his intentions, Mr. Giuliani’s statement reflects the ease with which people dissociate Mr. Obama and other African-Americans with American identity, especially those who don’t like him. A 2005 study examined this pattern using the Implicit Association Test, which measures the associations between concepts using differences in response timing during a categorization task. People tend to respond faster when categorizing paired stimuli that are congruent with their implicit associations (for instance, “thin people” or “good” versus “fat people” or “bad”) than those that are incongruent (the opposite pairings). In the study in question, the authors found response timing patterns that suggested that African-Americans as a group are “less associated with the national category ‘American’ than are white Americans” relative to the category “foreign” — a pattern that holds for other nonwhite groups such as Asian-Americans and Latinos.

These tendencies seem to translate into perceptions of Mr. Obama as being less American among his opponents. A study conducted during the 2008 election reported that supporters of both Mr. Obama and John McCain tended to implicitly associate their preferred candidate more closely with America, but these tendencies were especially pronounced among Republicans, who were “far more likely to dissociate Obama from the nation … than Democrats did with McCain.” The pattern of associating Mr. Obama with America less than political counterparts like Mr. McCain and Hillary Clinton was found in another study to be stronger when Mr. Obama’s race was highlighted.