RENO, NEVADA (NYTIMES) - Former vice-president Joe Biden delivered his most forceful response yet to President Donald Trump's attacks on him and his son, denouncing what he called a campaign of "lies, smears, distortions and name calling" in a speech here on Wednesday (Oct 2) night.

Mr Biden made his comments during a campaign swing through Nevada after days of internal debate among his advisers over how best to refute unsubstantiated claims by the president that Mr Biden improperly assisted his son Hunter's business ventures in Ukraine and China.

He said the attacks on his family were an attempt by the president to divert attention from the widening impeachment inquiry into Mr Trump's attempts to pressure Ukraine to investigate him - and cited them as proof that the White House feared him more than any other Democratic presidential contender.

"Let me make something clear to Trump and his hatchet men and the special interests funding his attacks against me: I'm not going anywhere," Mr Biden said at the Truckee Meadows Community College here, according to excerpts released before the speech.

"You're not going to destroy me," he said. "And you're not going to destroy my family. I don't care how much money you spend or how dirty the attacks get."

Earlier in the day, speaking at a gun safety forum in Las Vegas, Mr Biden excoriated the president and jokingly pretended to mispronounce the last name of his personal attorney, Mr Rudy Giuliani, who has communicated with Ukrainian officials on Mr Trump's behalf.

He said there was "zero, zero, zero" evidence that his family had done anything wrong.

Mr Biden's increasingly bitter fight with Mr Trump comes at a potential tipping point in the 2020 Democratic presidential race. Until recently, Mr Biden had led in most national polls since he entered the field last spring.

But Senator Elizabeth Warren of Massachusetts, fuelled by a highly disciplined campaign, has surged in many early-voting states, and even Mr Biden's aides concede that he remains prone to missteps and gaffes.

A Monmouth University Poll released on Wednesday showed that Mr Biden locked in a statistical dead heat with Ms Warren, who garnered 28 per cent support from Democratic and Democratic-leaning voters to his 25 per cent, a difference within the survey's margin of error.

Mr Biden and his advisers have been alarmed by reports that Mr Trump's supporters plan to launch an aggressive advertising campaign to portray the former vice-president, and not the president, as the person who acted improperly - despite the lack of any evidence to support that claim.

But Mr Biden's top advisers have been equally incensed by what they view as the news media's willingness to air unsupported allegations by Mr Trump and Mr Giuliani.

Mr Trump and Mr Giuliani have alleged that Mr Biden, as vice-president, pressured the Ukrainians to force out a top prosecutor in order to derail an inquiry into a Ukrainian company that paid his son Hunter. Mr Joe Biden was enforcing the demands of the Obama administration and other Western nations, who saw the prosecutor as corrupt.

On Sunday, Ms Anita Dunn and Ms Kate Bedingfield, two senior Biden strategists, wrote to several major TV networks asking them to stop booking Mr Giuliani, accusing him of spreading "debunked conspiracy theories".

Mr Biden amplified that argument on Wednesday, urging reporters to regard Mr Trump's statements, and his tweets, not as fodder for controversy but as a dangerous "abuse of power" that included enlisting foreign leaders as allies in his re-election effort.

"It's important to step back from the heated 24-hour news cycle and focus carefully on the larger story," he said, according to his remarks as prepared for delivery. "It's not about Donald Trump's antics. It's about what has brought Donald Trump, and the nation, to this sobering moment in our history - and to the choice facing us in 2020. What has brought us here is simply this: the abuse of power."

Mr Trump, he added, is "afraid of just how badly I would beat him next November".

The president does not agree. "I'd rather run against Biden than almost any of those candidates," Mr Trump told reporters at the White House.