Washington (AFP) - Donald Trump has launched a bitter broadside against Hillary Clinton depicting her as an "enabler" of Bill Clinton's past infidelities -- the latest nasty and deeply personal turn in the US presidential campaign.

Trump, who has all but locked up the Republican nomination, made the bizarre allegation while on the stump this weekend in an apparent bid to undercut his Democratic rival's appeal to women voters.

"Hillary hurt many women -- the women that he abused," Trump told a rally in Spokane, Washington late Saturday -- reiterating past criticism of Clinton over her handling of the former president's affairs.

"And just remember this, she was an unbelievably nasty, mean enabler, and what she did to a lot of those women is disgraceful."

"Some of those women were destroyed not by him, but by the way that Hillary Clinton treated them after everything went down."

The likely Republican nominee charged that Bill Clinton had "abused women more than any man that we know of in the history of politics."

"Bill Clinton was the worst in history, and I have to listen to her talking about it?" he thundered.

- Charges of misogyny -

Trump has accused Clinton, the presumptive Democratic candidate in November's presidential election, of using her gender to her political advantage -- playing the "woman's card" -- and says she would not be seen as a qualified candidate if not for her sex.

His remarks recalled one of the most contentious eras in American politics, when the nation was simultaneously riveted and revolted by the Monika Lewinsky sex scandal.

Clinton at first denied, but later acknowledged an affair with the White House intern, a scandal that ultimately led to his impeachment and deepened the partisan divide between Republicans and Democrats.

Trump's latest attack, reprising the sordid scandal, seemed designed to inoculate himself against anticipated charges of misogyny from the Clinton camp.

On and off the campaign trail, the tycoon has used crass and abusive language -- "bimbo," "dog," "fat pig" and other epithets -- to denigrate women he dislikes.

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The twice-divorced billionaire, who was celebrated for decades as one of New York's most sought-after bachelors, has also admitted to cheating on his first wife with the woman who became his second.

Clinton signaled in an interview broadcast on Sunday that attacks against Trump over his stance on women will definitely be part of her campaign battle plan.

"When he says, 'women should be punished for having abortions,' what does that mean? And how would he go about that?" the former first lady said on the "Face the Nation" program, referencing comments made by Trump earlier in the primary season.

- 'Ugly race' -

Over the past few days Trump has engaged in a Twitter war with US Senator Elizabeth Warren -- tipped by some as a possible Democratic running mate -- trading a stream of barbs and insults.

The former first lady said she would not engage in the mudslinging that helped her Republican rival vanquish his challengers for the nomination.

"I'm not going to run an ugly race. I am going to run a race based on issues," Clinton said.

"I don't really feel like I'm running against Donald Trump. I feel like I'm running for my vision of what our country can be, and to knock down all the barriers that stand in the way of Americans getting ahead."

But Clinton has labeled Trump a "loose cannon" for his erratic policy pronouncements, while he nicknamed her "crooked Hillary" in an allusion to the scandal over her use of a private email server as secretary of state.

Questioned by CBS over reports the FBI was expected to interview her as part of its probe into her email use, Clinton said she had not been approached.

"No one has reached out to me yet," Clinton said, adding: "I made it clear I'm more than ready to talk to anybody, anytime."

She went on to press for the real estate mogul to show similar transparency and release his tax returns ahead of the election.

"So what's there?" Clinton asked. "He owes it to the American people."

US political pundits are closely watching how Clinton responds to the escalating attacks from Trump, who has felled one opponent after the other with his brawling, no-holds-barred style of campaigning.

Howard Dean, who several years ago led a failed insurgent campaign for the Democratic presidential nomination, said the best strategy for the former secretary of state is counterattack, then take the high road.

"She needs to smack him hard, because everybody wants a strong president. But then she needs to pivot away from Trump, not engage and talk about her positive platform for America," Dean told MSNBC on Sunday.

The challenge, he acknowledged, is that while Clinton tries to put out a positive message, "the media will only focus on the sex scandal."