While Trump's core businesses have been suffering from losses and his net worth has declined, there is no evidence it is because he became president.
Reuters debunked his claim saying there is no evidence to indicate that Trump lost billions after becoming president citing Forbes Magazine's assertion that his net worth of $3.1 billion had not changed from the previous year.
"While Trump’s personal fortune held steady over the past year, he vaulted higher on the Forbes list of the world’s richest people as dozens of his fellow tycoons suffered financial setbacks while his real estate holdings held their value better," the report said.
In Oct. 2018, based on the Forbes 400 list, NBC reported that Trump's net worth had fallen since becoming the president. Forbes attributed the decline of Trump's fortune to three main factors: e-commerce eating into the value of Trump's real estate holdings, the intrusion of heightened security at Trump's resorts, and Trump's own over-reporting of the size of his penthouse.
Forbes 400 list released in 2020 revealed that Trump’s ranking had dropped to 352 from 275 in the previous year, and his net worth fell to $2.5 billion from the preceding year’s $3.1 billion. Forbes attributed the drop to the impact of the COVID-19 pandemic on the real estate and hospitality sector.
According to Investopedia, determining Trump's exact net worth and income are difficult as he has refused to publish his tax returns, and that approximations from outlets such as Forbes are probably the closest estimates.
A New York Times investigation published in Sept. 2020 based on Trump's tax information of more than two decades obtained by the team revealed that contrary to the image of a successful real estate empire, Trump's core businesses have been suffering from heavy losses. While publicly available figures suggest that Trump's businesses aren't in great financial shape, there is no evidence to suggest that his net worth and wealth declined primarily because of him making a switch from being a businessman to holding the president's office.