Former and current US presidents Bill Clinton and Barack Obama join the campaign trail Tuesday for Hillary Clinton, standing in for the Democratic White House hopeful while she recovers from pneumonia.

Clinton is set to return to the fray on Friday after several days of rest when she attends a Black Women's Agenda symposium Friday in Washington, with less than eight weeks to go before the election, the campaign announced.

With Republican rival Donald Trump in striking distance in national polls and some battleground states, Clinton has suffered perhaps the worst week of her 15-month quest to become America's first female president.

On Friday, she sparked a firestorm when she called half of Trump's supporters as ‘deplorables’ and then her campaign failed to be transparent when she fell ill at the weekend.

Clinton, 68, sought to draw a line under the health scare rocking her campaign.

‘I just didn't think it was going to be that big a deal,’ Clinton told CNN late Monday when asked why she kept her Friday pneumonia diagnosis under wraps until Sunday, when she fell ill at a 9/11 memorial event at Ground Zero in New York.

‘It's just the kind of thing that if it happens to you and you're a busy, active person, you keep moving forward.’

She has expressed a desire to swiftly rejoin the race and said she will resume campaigning within the ‘next couple of days.’

In the meantime, her husband Bill takes over for her in California, attending a fundraiser in Los Angeles while his wife rests at their home in Chappaqua, New York per her doctor's orders.

He also will campaign for her Wednesday in Las Vegas.

She gets a further boost when Obama hits the campaign trail for her in Philadelphia on Tuesday.

- We 'take responsibility' -

Facing intensifying scrutiny about her health, the Democrat will also release more medical records, as her team acknowledged it stumbled when it failed to alert the press and public about Clinton's condition in a timely way over the weekend.

Discussing the event itself, Clinton explained: ‘I felt dizzy and I did lose my balance for a minute.’

The incident -- captured on amateur video -- gave Trump, 70, a new opening to question the former secretary of state's fitness for the nation's highest office as the race intensifies.

Trump and his team have wished Clinton a rapid recovery. But his campaign manager Kellyanne Conway directed stinging criticism at Clinton Tuesday.

‘I think she had a terrible week. She certainly had a terrible weekend. Not because she's sick,’ Conway told CNN. ‘We're glad she said she's feeling better.’

She stressed instead that ‘transparency and trustworthiness are her two pillar problems,’ and that Clinton suffered ‘the worst 48 hours of her campaign.’

Clinton admitted: ‘If we weren't fast enough, you know, I've talked to my staff. We, you know, take responsibility for that.’

But she quickly insisted she has been far more transparent than Trump.

‘The information is out there. You can't say the same thing about Donald Trump,’ she said, adding that Americans ‘deserve to know what he's up to and what he is hiding.’

Trump has promised to release medical records as early as this week, once test results are back.

- 'Catastrophic insult' -

Meanwhile, his running mate Mike Pence, the Indiana governor and a former congressman, met with House Republicans on Capitol Hill on Tuesday and said he and Trump were ‘grateful’ for the support from GOP lawmakers.

But he also turned to Clinton's Friday remark that ‘half’ of Trump's supporters were in a so-called ‘basket of deplorables’ because they were racist, misogynistic and xenophobic.

‘This was a catastrophic insult to the American people,’ Pence told reporters as he again demanded Clinton ‘retract those offensive statements and apologize.’

Clinton has expressed regret for saying ‘half’ but also said she would not back down from calling out ‘racist rhetoric’ on the campaign trail.

Pence also rejected accusations that Trump's campaign was courting white supremacists including former Ku Klux Klan leader David Duke, who has endorsed Trump.

‘Donald Trump and I have denounced David Duke repeatedly,’ Pence said. ‘We have said that we do not want his support, and we do not want the support of people who think like him.’

The brash billionaire's campaign has courted controversy from the start, and sporadic clashes have erupted at his rallies between supporters and anti-Trump protesters.

An altercation erupted Monday night at a Trump rally in Asheville, North Carolina, where video shows a Trump supporter, his fists raised, yelling at and pushing a protester before slapping his face.