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 about his lack of support from black voters, he said, “I think we need to do better.” Buttigieg’s plan to boost the diversity of his backers was centered on a breathtakingly cynical ploy. The really dispiriting part is that it worked. "It's not rude to eat with my hands?" Buttigieg asked as he looked at fried chicken, collard greens, and mac and cheese at Harlem’s famous soul food joint Sylvia’s. He took the subway uptown in late April. Sitting across from him was Al Sharpton, a controversial figure who should have lost any legitimacy long ago, but who has now...