So far, Pete Buttigieg has made it look easy. The once little-known former mayor of a midsize Midwestern city vaulted over a former vice president and several U.S. senators in the Iowa caucuses and New Hampshire presidential primary. The 38-year-old’s fresh face, intellect and turn-the-page message won votes across many demographic groups in the kickoff states. Now the promise of his candidacy is colliding with the reality of the central question about his viability: Can he win among minority voters who form the critical foundation of the party’s base? That will be tested Saturday in Nevada, with a diverse blend of Latinos and African Americans, but especially in South Carolina, where two-thirds of the primary electorate could be black voters, the base of the Democratic Party that Buttigieg has struggled to attract. Buttigieg’s strategy is to earn a fresh look from black and brown voters by flashing his support in the first two contests, drawing on the validation of minority leaders who have endorsed him and leveraging the personal networks of his supporters. With the South Carolina primary rapidly approaching Feb.