Very long article included below. Short summary:
"Donald J. Trump paid $750 in federal income taxes the year he won the presidency. In his first year in the White House, he paid another $750.
He had paid no income taxes at all in 10 of the previous 15 years — largely because he reported losing much more money than he made." Many of his deductions appear to be legally questionable (e.g. declaring the family's vacation home as an investment property, in order to deduct much of its expenses), and the IRS audit which he keeps mentioning appears to be related to a dubious interpretation of an Obama-era tax law; Trump used that interpretation to claim additional annual losses of over $70 million, which he's rolled over to future years to eliminate paying any income taxes.