Pete Buttigieg needed to connect with black voters. Or, more precisely, he needed black voters to know that he knew that he needed to connect with black voters. Buttigieg is known on the campaign trail as “Mayor Pete,” partly out of faddish familiarity and partly thanks to the burden of a last name that doesn’t roll off the tongue. (His supporters have taken to wearing T-shirts that serve as pronunciation guides, BOOT-EDGE-EDGE.) He has rocketed up the Democratic presidential charts to No. 4, behind former Vice President Joe Biden, Sen. Bernie Sanders of Vermont, and Sen. Elizabeth Warren of Massachusetts. Not bad for the 37-year-old Rhodes scholar, Navy intelligence veteran, and mayor of South Bend, Ind. But even as he drew larger and larger crowds, the candidate’s support was, well, pale. When asked in April...