WASHINGTON - Weakened by damning revelations about his taxes, Republican Donald Trump has intensified his personal attacks on Hillary Clinton as he scrambled Monday to counter his rival’s substantial gains in the White House battle.

The Democrat Clinton has surged in recent polling following their first debate, pushing the brash billionaire Trump onto his heels with just 36 days to go before the November 8 election.

The pair were visiting America’s battleground states Monday: Trump addressed military veterans in Virginia before a rally later in Colorado, while his rival Clinton was travelling to key swing state Ohio. Following what Clinton’s campaign described as “his worst week yet” — culminating with the leak of documents suggesting he may have paid no income tax for two decades — Trump revived his attacks on the former secretary of state’s handling of classified information via a “basement” email server.

“Hillary Clinton’s only experience in cyber-security involves her criminal scheme to violate federal law, engineering a massive cover-up and putting the entire nation in harm’s way,” he said.

But Trump also broke new ground in the violence of his personal attacks on Clinton at the weekend, mocking her for coming down with pneumonia last month and even openly questioning her loyalty to her husband.

“Here’s a women who’s supposed to fight trade deals in China... she’s supposed to fight all of these different things, and she can’t make it 15 feet to her car. Give me a break,” Trump said Saturday night in Manheim, Pennsylvania as he imitated Clinton stumbling into her vehicle during a 9/11 ceremony in New York. “Hillary Clinton’s only loyalty is to her financial contributors and to herself,” he said.

“I don’t even think she’s loyal to Bill, if you want to know the truth. And really, folks, really, why should she be, right?” said the Manhattan billionaire, who has revived talk of Bill Clinton’s past infidelities in the wake of his lackluster performance in last week’s debate.

Even as he launched the contentious new attacks, a defiant Trump campaign dodged swirling questions about his tax record.

Without admitting fault, Trump’s top allies praised their candidate’s business acumen following the bombshell revelations by The New York Times focusing on the real estate mogul’s massive 1995 losses and his clever use of the US tax code.

If true, the report is proof of the tycoon’s “absolute genius,” said former New York mayor Rudy Giuliani, a key Trump surrogate.

“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 Sunday.

According to documents obtained by the Times, Trump declared a loss of $916 million on his 1995 tax return, enabling him to legally avoid paying taxes for up to 18 years.

Trump has refused to release his tax returns, something US presidential candidates have done for four decades.

In their September 26 presidential debate, Clinton suggested that Trump is hiding “something terrible” by failing to produce his tax returns, and suggested that he had not paid any federal income tax.

Trump’s answer: “That makes me smart.”

He reportedly took massive, though legal, tax breaks on failing businesses, earning millions while shareholders and investors swallowed the losses and contractors went unpaid.

Clinton seized on the Times report as undercutting Trump’s core argument: that he is an iconic business success whose acumen can translate into positive action in the White House.

“Can a man who lost $1 billion in one year, stiffed small businesses, and may have paid no taxes really claim he’s ‘good at business’?” she tweeted Monday.

The tax scandal marked a low point in a bruising week for Trump in which he lost the momentum gained over the previous month and was seen as having stumbled in the debate.

An ABC News/Washington Post poll Sunday said 53 percent of Americans saw Clinton as the debate winner, compared to 18 percent for Trump.

A nationwide poll released Monday by Politico and Morning Consult showed Clinton with 42 percent support from likely voters compared to 36 percent for Trump, a four-point Clinton gain from the previous week.

Tuesday will see the vice presidential nominees clash in their only debate of the election cycle, with Republican Mike Pence, the governor of Indiana, and Democratic Senator Tim Kaine of Virginia tangling on issues likely to include abortion, climate change and trade — before the nominees themselves face off in their second debate on Sunday.