Late last year, in a Miami conference room, a consultant for President Trump’s company said business at his prized 643-room Doral resort was in sharp decline. At Doral, which Trump has listed in federal disclosures as his biggest moneymaker hotel, room rates, banquets, golf and overall revenue were all down since 2015. In two years, the resort’s net operating income — a key figure, representing the amount left over after expenses are paid — had fallen by 69 percent. Even in a vigorous economy, the property was missing the Trump Organization’s internal business targets; for instance, the club expected to...