She has denounced him as a bully, humiliating her for gaining weight.
And, in a pre-dawn Twitter tirade on Friday, Republican Presidential candidate Donald Trump hit back with a vague, unsubstantiated claim about former Miss Universe Alicia Machado from Venezuela and a sex tape.
This is the hot topic in the US election campaign, with less than six weeks to go.
Trump’s attacks provided critics with new fodder to question his temperament for the White House.
“Did Crooked Hillary help disgusting (check out sex tape and past) Alicia M become a US citizen so she could use her in the debate?” Trump said in his Twitter messages in the early hours of Friday.
He did not elaborate on his allegations beyond saying that the Clinton campaign was unaware of the beauty queen’s past and had been “duped” by her.
Democratic Presidential candidate Hillary Clinton, who first referenced Machado in Monday’s TV debate, expressed shock at Trump’s ‘middle of the night’ Twitter onslaught.
“His latest Twitter meltdown is unhinged, even for him,” she told a campaign rally in Coral Springs, Florida.
“It proves yet again that he is temperamentally unfit to be president and commander-in-chief.”
Trump, the former owner of the Miss Universe pageants, also branded the former beauty queen ‘disgusting’.
He has suggested he might attack Hillary Clinton in the next debate on the infidelities of her husband, ex-President Bill Clinton.
And on the campaign trail in Novi, Michigan, he was also lashing out over money.
“Hillary Clinton has made a living raking in donations from special interests that have raided our factories and ripped the jobs straight out of Michigan and every other state,” he told supporters.
“That is how she gets rich, by taking your jobs and your money away from you and away from your state.”
Trailing in the polls after a debate he is widely seen to have lost, Trump could see his beauty queen outburst
damage his already weak standing among women and Hispanics.