Tim Kaine, the Democratic vice-presidential nominee, has accused Donald Trump of "chumming around" with racists and bigots, in endorsing Hillary Clinton's claim that half of the Republican hopeful's supporters comprise a "basket of deplorables".
Mr Trump has used the "deplorables" comment, made at a fundraiser, as his central line of attack in recent days. And despite the comment being widely perceived as a major gaffe, the Clinton campaign appears eager to pick a fight.
Mrs Clinton has insisted that she was right in labelling many Trump supporters "racist, sexist, homophobic and xenophobic", even as she said she was wrong to say "half" ascribe to those views.
With the former secretary of state off the campaign trail to recover from pneumonia, Mr Kaine picked up the torch and ran with it yesterday (Tuesday).
"If you're chumming around with the head of the Ku Klux Klan or people that have that type, that's deplorable," he said, referring to David Duke, a white supremacist and vocal Trump supporter.
The remark came after Mike Pence, Mr Trump's running mate, denounced Mr Duke's support but refused to label him "deplorable".
"If you cannot call out bigotry, if you cannot call out racism, xenophobia... if you can't call it out and you stand back and you're silent about it, you're enabling it to grow," Mr Kaine said.
Eager to discuss anything other than Mrs Clinton's health, her allies are trying to make the case that supporting Mr Trump means linking arms with the likes of Mr Duke.
But Mr Trump clearly believes the debate over the "deplorables" comment works to his advantage.
At a rally on Monday, he said he was "shocked and alarmed" to hear Mrs Clinton "attack, slander, smear, demean these wonderful, amazing people". He added: "We have the support of cops and soldiers, carpenters and welders, the young and the old, and millions of working-class families who just want a better future and a good job," he said. "These were the people Hillary Clinton so viciously demonised."
He called on Mrs Clinton to apologise and has released a TV advert attacking her over the remark, as well as a fundraiser letter asking supporters to defend the "tens of millions of Americans Hillary called 'deplorable'?"