The news in Sunday's New York Times on ended a disastrous week for the Republican presidential candidate, focusing renewed attention his steadfast refusal to release his income tax returns.
Former New York mayor Rudy Giuliani, a key Trump surrogate on the campaign trail, called the revelations proof of the New York tycoon's "absolute genius."
"You have an obligation when you run a business to maximize the profits and if there is a tax law that says I can deduct this, you deduct it," Giuliani told ABC News, suggesting investors in Trump's company probably would have sued him had he done otherwise.
Bernie Sanders, Hillary Clinton's vanquished Democratic presidential primary foe who now supports her, took the opposite view.
"If everybody in this country was a 'genius'," he told ABC, "we would not have a country," the Vermont senator said.
Trump tweets again
Trump, while not admitting to paying little or no taxes, boasted on Twitter that his deftness in fiscal and business dealings is one of his greatest strengths.
"I know our complex tax laws better than anyone who has ever run for president and am the only one who can fix them," he wrote in a tweet after The Times story appeared.
The real estate mogul declared a loss of nearly $1 billion on his 1995 income tax return, enabling him to legally avoid paying taxes for almost two decades, according to documents obtained by the New York daily.
He repeatedly has refused to make his tax filings public -- the first major party presidential contender to fail to do so since Richard Nixon in the 1970s.
Trump has said he will release his tax returns only after federal authorities complete an ongoing audit.
However, US tax officials -- without confirming or denying that Trump's tax filings are under review -- have said being under audit does not prevent their release.
A lawyer for Trump, meanwhile, said publication of Trump's tax returns is illegal because he did not authorize it, and threatened "appropriate legal action" against The Times, the paper reported.
During last week's acrimonious first presidential debate, Clinton suggested that in failing to produce his tax returns, Trump is hiding "something terrible."
"Maybe he doesn't want the American people, all of you watching tonight, to know that he's paid nothing in federal taxes," she said during Monday night's debate, prompting Trump's retort: "That makes me smart."
Numerous reports have suggested Trump has used high-pressure tactics to convince officials in New York and elsewhere to give him tax breaks and other hugely favorable conditions in his deals.
He is also reported to have taken massive, albeit legal, tax breaks on failing businesses, earning a fortune while shareholders and investors swallowed large losses and contractors went unpaid.
Clinton's campaign manager Robby Mook with barely suppressed glee, noted in an interview Sunday that this latest campaign trail "bombshell" follows an abysmal few days for the real estate mogul.
'Out of control'
"Trump has had a really bad week: He failed in the debate. He has spun out of control subsequent to that. Insulting (Venezuela-born beauty queen Alicia) Machado. His 3 am tweet storm," Mook said, recounting other Trump controversies that dominated headlines last week.
"You know, his campaign is spinning out," he said.
In the latest poll showing a boost for a newly energized Clinton this week, an ABC News/Washington Post survey released on Sunday said 53 percent of Americans saw Clinton as the winner, compared to 18 percent for Trump.
Nearly half of respondents said he got his facts wrong and a third that he outright lied, while his unpopularity rating grew to 64 percent in the same poll, compared to 53 percent for Clinton.
Trump spent most of last week embroiled in controversy over his abusive comments about Machado, the Venezuela-born beauty who won the Miss Universe pageant -- which was owned by Trump at the time -- in 1996.
Trump doubled down this week, including in a predawn Twitter rant Friday with more insults about Machado -- a tirade that Clinton said proves he is "temperamentally unfit" for the presidency.
Trump then went on the attack again on Saturday, mocking the former first lady for a recent bout with pneumonia and raising questions about her loyalty to her husband, former president Bill Clinton.
His running mate Mike Pence is set to debate his Democratic counterpart Tim Kaine on Tuesday, but Americans are expected to pay little attention, with the focus firmly on Trump with little more than a month to go before the November 8 election.
