Donald Trump Jr. and Ivanka Trump, pictured here at their father's inauguration in January, are key members of his support system

The younger Donald Trump delivered a blistering performance Thursday on Fox News, calling Democrats' emphasis on his father's alleged Russia ties 'a 10-month witch hunt'

In business as in the White House, Donald Trump leans on family. While daughter Ivanka deflects criticism by projecting tolerance on social issues, elder brother Donald Jr. has come out swinging for his father.

When Trump jets off to his New Jersey golf club on Friday, he leaves behind a US capital buzzing after the dramatic testimony from sacked FBI director James Comey about what he called the US president's 'very concerning' behavior.

Just a week ago, the president had sparked global outcry over his decision to walk away from the Paris climate accords, defying months of apparent lobbying from Ivanka, an unpaid White House advisor and long his close confidante.

But if Ivanka kept her head down a week ago – by not attending the Paris announcement, which coincided with the Jewish holiday of Shavuot – her elder brother moved center stage as Comey testified on Thursday.

Don Jr. blasted out a Twitter tirade and delivered a fiery television appearance as the 70-year-old president stayed uncharacteristically silent on Twitter, allowing his son and personal lawyer to do all the talking.

'This has been a 10-month witch hunt,' he told Fox News. 'Give the guy a chance. Let him do what he was elected to do and he will do a phenomenal job.'

'You see how disgusting the swamp really is,' he followed up, in a nod to his father's 'Drain the Swamp' slogan about cleaning up Washington.

'It's going to make 2020 that much easier.'

Trump Jr. tweeted on Thursday while fired FBI director James Comey called his father a liar during a public Senate hearing

Donald Trump, Jr was a respected surrogate for his father during his White House run

Intelligent, articulate and with the bravado typical of a New York businessman, it was a return to the spotlight for Don Jr., a respected surrogate during last year's campaign who is thought to harbor political ambitions of his own.

Analysts say it is natural for the president to lean on his family.

'It makes sense, given that Trump himself can't get involved in talking about the investigation now that there is a special prosecutor,' says Ronald Kessler, an author, former investigative reporter and friend of the president.

'He is very close to his family,' agreed Jeanne Zaino, a professor of political science at Iona College.

'Trump Jr. was really being the mouthpiece of his father, saying exactly what his father would have said would he have been able to tweet,' she told AFP.

To many on both sides of the political divide, Don Jr. and Ivanka have been reasonable and more measured than their father – devoted surrogates who could each have political futures if they desired.

It was telling in last year's toxic election campaign, when Democratic opponent Hillary Clinton replied: 'His children,' when asked for one thing she respected about Trump, praising them as 'incredibly able and devoted.'

Ivanka Trump, a businesswoman and mother of three, prefers not to engage in attack-dog politics

The president's son defended his father over and over on Twitter, and has become one of his most skilled surrogates both online and off

Of course, Don Jr.'s sudden explosion back onto the scene does not mean Ivanka is suddenly out of favor after the climate change fallout.

'There is no way that the kids are ever going to feel any estrangement from their father,' Kessler told AFP.

'Ivanka is not a tweeter like her father,' said Zaino. 'It's not a surprise he turned to somebody else – it would not be a good use of her public image and the work they have her doing,' she explained.

The 35-year-old mother of three, former model, businesswoman and reputed favorite child prefers to stay away from attack-dog politics.

Photographed leaving her home for the White House in a parade of dresses and shoes from her label, she carefully cultivates a more moderate image, returning to Twitter after the climate decision to voice her support for LGBT rights.

Regular photographs of her children posted on her social media accounts also evoke a softer side to the Trump family – a tactic that Don Jr. has also favored.

But if both children's futures depend on how their father's presidency plays out, Don Jr. also treads a fine line between politics and the business.

Running The Trump Organization with younger brother Eric in their father's absence, they are not supposed to discuss business with their father – an arrangement that came under fire from political opponents and ethics experts.

'So far so good, but its only been a few months,' said Zaino.