WASHINGTON — A New York Times report that President Donald Trump paid just $750 in federal income tax the year he entered the White House — and, thanks to colossal losses, no income tax at all in 11 of the 18 years that the Times reviewed — served to raise doubts about Trump’s self-image as a shrewd and successful businessman. That Sunday’s report came just weeks before Trump’s re-election bid served to intensify the spotlight on Trump the businessman — an identity that he has spent decades cultivating and that helped him capture the presidency four years ago in his first run for political office.