This Thanksgiving, Americans in general — and free-market conservatives in particular — have plenty for which to be grateful. And much of it would be absent had the White House’s current occupant not become president on November 8, 2016. The day after Donald J. Trump defeated Hillary Clinton, Princeton University economist Paul Krugman called Trump’s victory “the mother of all adverse effects.” He predicted “very probably . . . a global recession, with no end in sight.