You will note the Republican candidate also has problems with his background.

Pete Buttigieg rose from small-city obscurity to the top of Iowa’s presidential polls by saying yes to every interview and presenting himself as an aggressively transparent candidate poised to take on President Trump and his array of known and unknown conflicts.

Yet the South Bend, Ind., mayor now faces cascading questions he has been unable to answer about his work at McKinsey & Company, the management consulting firm that accounts for the entirety of his private-sector career. He hasn’t revealed his clients, citing a nondisclosure agreement he signed at the outset of his employment.

The three years Mr. Buttigieg spent at McKinsey represent one-fifth of his professional resume. His campaign on Friday night for the first time disclosed broad strokes beyond the most elemental details of his work, some of which he also discussed in his memoir, which was published in February.

The pressure to disclose more about his work at McKinsey comes as the 37-year-old mayor also faces increased scrutiny about his lack of appeal to African-American voters, and amid increasing calls from Senator Elizabeth Warren of Massachusetts, who does not hold closed-door fund-raising events, to reveal details about his campaign’s fund-raising operation — including the names of his bundlers.