Three factors are at play. Much of that decline is due to deeper reporting, which revealed, for example, that the president had been lying about the size of his penthouse. Some of it is due to larger market forces. Trump owns commercial space at a time when e-commerce is decimating brick-and-mortar retail, shaving more than $100 million off his fortune—and no amount of bully-pulpit Amazon-bashing will change that.
But the third factor comes from how Trump the president affects Trump the brand. Those familiar with him saw his 2016 run as a surreal marketing strategy, and Trump has said as much, telling Fortune way back in 2000, “It’s very possible that I could be the first presidential candidate to run and make money on it.” Since his unexpected ascent to the White House, Trump has tried to leverage the trappings of the presidency to benefit his commercial projects, from visits to his golf courses to hosting summits at Mar-a-Lago to launching a new hotel-licensing business aimed at his voters. (The Trump Organization denies the licensing business has to do with politics.)
“My father made a tremendous sacrifice when he left a company that he spent his entire life building to go into politics,” counters Eric Trump, who now comanages the Trump Organization on behalf of the president, in a statement to Forbes. “Everything he does is for the good of the American people—he has zero involvement in the Trump Organization and quite frankly to suggest otherwise is outrageous.” (Eric Trump himself, however, told Forbes shortly after the inauguration that he would provide the president bottom-line updates “probably quarterly.”)