Trump questions Clinton's mental health

Donald Trump has unleashed a series of nasty personal attacks against his Democratic opponent, Hillary Clinton, mocking her appearance and questioning her mental health several times during a New Hampshire campaign rally and on social media.

"She is a totally unhinged person. She's unbalanced. And all you have to do is watch her, see her, read about her," Trump said during a campaign rally in Windham, New Hampshire. "She will cause - if she wins, which hopefully she won't - the destruction of our country from within."

The GOP presidential nominee called Clinton unstable and incompetent several times throughout the rally. At one point, he also called her "Hillary Rotten Clinton," a play on her maiden name, Rodham.

The attacks went far beyond what is considered appropriate or dignified in political discourse. And notably, his most vitriolic attacks focused specifically on ad hominem attacks rather than on policy differences.

"I think the people of this country don't want somebody that's going to short-circuit up here," Trump said, pointing to his head. "Not as your president, not as your president."

"Now you tell me she looks presidential, folks. I look presidential," he said in another instance.

Trump said Clinton is a "dangerous liar" and accused her of failing to achieve anything during her long career in public service - except, he said, avoiding criminal charges for using a private email server during her tenure as Secretary of State.

The FBI cleared her of criminal wrongdoing after a lengthy investigation but nonetheless sharply criticised her handling of classified information over email.

Clinton was blasted by reporters for recently mischaracterising FBI Director James Comey's comments about whether her public statements about the emails were truthful.

She explained during a question-and-answer session in Washington that she had "short-circuited" when giving the initial response, a phrase which Trump repeatedly parodied.

"Honestly, I don't think she's all there," Trump told the crowd in Windham.

Trump's most forceful policy-oriented attack focused on Clinton's support for the 2003 invasion of Iraq, using her vote as a US senator from New York to call her foreign-policy judgment into question. Trump wrongly claimed, as he often does on the campaign trail, that he did not support the Iraq War. That claim has been repeatedly proved false.

The real estate mogul has regularly used Clinton's support for the war in Iraq and her support for intervening in Libya - both of which he supported - to question her qualifications for the presidency. Attempting to neutralise her attacks against his character and qualifications, Trump has sought to undermine her decision-making skills while painting her as an out-of-touch member of the Washington political establishment.

Honestly, I don't think she's all there

Donald Trump

"I've always had a great temperament. And you know, I win. I have a winning temperament. We're going to win, we're going to start winning again," he said.

"But I've won. My whole life has been about winning. I win. She can't win. She's not a winner. She can't win."

His remarks onstage came after his campaign released a nasty video on Facebook suggesting that Clinton is a malfunctioning robot.

"Is Robot Hillary melting down?" said the video's opening caption.

The short video features Clinton misspeaking and correcting herself on several occasions. The video eventually cuts to a clip of Clinton's "I may have short-circuited" quote.

At the end of the footage, video graphics render sparks spewing from Clinton's mouth.