Donald Trump

And on Thursday, Jimmy Fallon asked if he could mess it up.

First, Trump winced and grimaced, shaking his head as the "Tonight Show" audience erupted in a smattering of applause and cheers.

Moments later, the Republican nominee relented.

"The answer is yes, but the people in New Hampshire, where I'm going to be in about an hour from now, I hope they're going to understand," Trump said. "Go ahead."

Trump's signature coif has long been the subject of intense scrutiny, including from those who've questioned whether Trump's do is the real thing.

The Republican candidate had been a leader of the "birther" movement that questioned Hawaii-born Mr Obama's citizenship.

But his campaign now accuses his Democratic rival Hillary Clinton of introducing the "smear" during the 2008 Democratic nomination contest.

There is no evidence to link Mrs Clinton to the birthers.

In reaction she tweeted that President Obama's successor "cannot and will not be the man who led the racist birther movement".

As the campaign enters its final stretch, some of Donald Trump's children are showing signs of impatience and struggling to stay on message.

In the past 24 hours, Ivanka Trump and Donald Trump Jr. have cut off interviews when pressed for answers on tough questions. Trump Jr. strayed from the campaign's talking point about the Republican nominee's tax returns -- that they'll be released once an IRS audit concludes -- when he said unveiling the documents would "detract" from his father's message.

Mr Trump released the letter following a recent physical examination by Dr Harold N Bornstein.

The 70-year-old is listed as 6 foot 3 inches (1.9 metres) and weighs 236 pounds (107 kilos).

The letter comes as his rival Hillary Clinton returns to the campaign trail after time off with pneumonia, appearing briefly to reporters.

Boarding a plane in White Plains, New York, she spoke to journalists as she heads to North Carolina to hold a rally, her first campaign event since the weekend.

Mr Trump said health had now become "an issue" in the election campaign.

Mrs Clinton was taken ill on Sunday at a 9/11 memorial ceremony and cancelled a campaign trip to California.

She will also be releasing new medical records to help ease concerns about her health, a campaign spokesman said.

"There's no other undisclosed condition. The pneumonia is the extent of it," Brian Fallon told MSNBC.

He said she would probably resume campaigning in the next few days.

Mrs Clinton said on Twitter she was "anxious" to return to the trail.

Dr Lisa Bardack said she was diagnosed with pneumonia on Friday and given antibiotics, but had become dehydrated at the New York event.

Video shows her being supported by aides as they put her into her van after she left the ceremony early.

The doctor's statement said she was now re-hydrated and "recovering nicely".

"Secretary Clinton has been experiencing a cough related to allergies. On Friday, during follow up evaluation of her prolonged cough, she was diagnosed with pneumonia," Dr Bardack's statement said.

But the Democrat launched a furious attack on her Republican opponent and promised to keep fighting "bigotry and racist rhetoric".

Mr Trump had responded by saying the comment was "insulting" to "millions of amazing, hard working people".

Opinion polls suggest Mr Trump is gaining on Mrs Clinton.

The rivals are neck and neck in the key battleground states of Ohio and Florida.

Speaking at a fundraiser, she said they were "racist, sexist, xenophobic, Islamophobic - you name it".

She then went on to say the rest of the Republican nominee's supporters were "just desperate for change".

Mr Trump's campaign manager said Mrs Clinton had insulted "millions of Americans", with her comments.

Polls released earlier this week suggest Mr Trump is gaining on Mrs Clinton, and the rivals are neck-and-neck in the key battleground states of Ohio and Florida.

In other developments:

The move makes him the third largest publicly-disclosed donor in the 2016 election cycle.

Moskovitz and his wife Cari Tuna said in a post on Medium that they will divvy up the funds among a number of PACs, including the Hillary Victory Fund and MoveOn.org’s political action arm. The largest contributions of $5 million will go toward the League of Conservation Voters, an environmentalist group, and For Our Future, a PAC organized by labor and environmental groups.

"And by the way, with Iran, when they circle our beautiful destroyers with their little boats and they make gestures that our people -- that they shouldn't be allowed to make, they will be shot out of the water," he said at a rally here.

Taking such action would have tremendous ramifications and would likely be considered an act of war. The comments, even given Trump's penchant for tough language, are unusual for a presidential candidate.

Trump appeared to be referring to a series of close encounters between the US and Iran in international waters in the Persian Gulf.