WASHINGTON, United States (AFP) — President Donald Trump reeled Monday on the eve of his first televised debate against challenger Joe Biden after a bolt-from-the-blue report showed he has been avoiding paying almost any federal income tax for years.

The scoop from The New York Times, reporting that Trump paid only US$750 in federal income tax in 2016 and 2017, and none at all for 10 of the previous 15 years, was a shot to the jugular of the self-described billionaire.

Throughout his unlikely rise to power, Trump has portrayed himself as a hard-nosed businessman on a mission to drain the Washington swamp and represent what he calls “the forgotten man and woman”.

Trump calls the Times’ story — which the newspaper says is based on his long secret tax returns — false.

“The Fake News Media, just like Election time 2016, is bringing up my Taxes & all sorts of other nonsense with illegally obtained information,” he tweeted Monday.

But with several new polls on Sunday once again suggesting Biden has the upper hand, the Republican goes into the debate in Cleveland on Tuesday ever more on the defensive.

A Washington Post/ABC News poll put Biden 10 points ahead of Trump nationally, at 53 to 43 per cent support among registered voters, while an NBC News-Marist poll gave the Democrat a similar lead, of 54 to 44, in key swing state Wisconsin — which Trump had carried in 2016.

Trump’s Democratic challenger is homing in on the president’s handling of the coronavirus pandemic and his controversial rush to fill the Supreme Court seat left vacant by the late liberal justice Ruth Bader Ginsburg.

But the tax report threatens the core of Trump’s political identity — that vaunted ability to connect with blue collar voters.

Biden, who frequently touts his early boyhood years in the hardscrabble Pennsylvania town of Scranton, has been trying to reframe the populist leader as a spoiled playboy from Manhattan.

Though its impact on voters was still far from clear, the Times’ report — which purports to reveal information that prosecutors and congressional investigators have been trying fruitlessly to obtain for years — hands Biden piles of new ammunition.

And the Democrat’s campaign immediately opened fire.

In a quickly crafted new ad, haunting piano music accompanies a montage of faces representing Americans in relatively low wage but admired jobs, listing the income tax they typically pay: US$7,239 for teachers, US$5,283 for firefighters, US$10,216 for nurses.

Switching to footage of the president, the text then reads: “Federal income taxes paid: Donald Trump US$750.”