Donald Trump is keeping it all in the family at this week's Republican convention, giving his four children prime speaking slots alongside his wife Melania and highlighting the unprecedented role they have played in the political affairs of the United States.

The children and spouses of US candidates normally partake in the rituals of presidential campaigns: Last week's virtual Democratic convention saw Joe Biden flanked by his children and grandchildren, who highlighted the qualities of their 77-year-old patriarch.

But the Trump side is markedly different, says political science professor Costas Panagopoulos, because the president's family members "can not only comment on the candidate and his character... but also on substance, on policy issues that they have been directly involved in during the administration."

"They have been closely linked to the administration or Republican politics and they have played important roles in governing," the scholar based at Northeastern University said.

"They are no longer family members, they are politicians and they are part of this administration."

Donald Jr, Ivanka and Eric Trump -- the three children the billionaire had with his first wife Ivana -- all either bear official White House titles or are ardent supporters of his policies and involved in his campaign.

The eldest, 42-year-old Donald Jr, stayed in New York with Eric to officially take over the family's Trump Organization while their father was off to Washington.

But he has simultaneously become a star of the Trump base, fiercely backing White House policies and routinely defending his father on Twitter, retweeting memes and conspiracy theories and developing his brand of provocation.

Heated critique

Monday evening the Trump scion -- who has hinted at his own political aspirations -- delivered a heated critique of the Democrats, accusing them of "attacking the very principles on which our nation was founded."

He said they were closing their eyes to "rioting, looting and vandalism" along with rising crime in major US cities.

Earlier in the evening his partner Kimberly Guilfoyle -- who was once married to California's Democratic governor Gavin Newsom but made a name as a Fox News host and now works for the Trump 2020 campaign -- delivered an impassioned rally-style speech to an empty auditorium.

Her voice rising, Guilfoyle's dark address warned that Democrats want to "enslave you to the weak, dependent, liberal" ideology.

On Tuesday it's Melania's turn to vouch for her husband: the first lady and third wife of the president will surely be keen to keep the pundits from bringing up her 2016 convention speech, which included phrases curiously similar to Michelle Obama's 2008 convention address.

Eric is also hitting the campaign trail for his father despite helming the family's Trump Organization conglomerate and dealing with legal battles related to the company.

He's expected to speak Tuesday along with his sister Tiffany -- Trump's only child with second wife Marla Maples -- before his wife Lara hits the stage Wednesday.

Ivanka Trump -- who with her husband Jared Kushner is a White House advisor -- will play a starring role on Thursday, introducing her father's nomination acceptance speech which will close the convention.

Where's Jared?

But some Trump clan members will not be in attendance: the president's niece Mary Trump, author of a recent book describing her uncle as a narcissistic liar, was not invited.

Her aunt Maryanne Trump Barry, Trump's 83-year-old sister and a formal federal judge, has also called her brother a liar.

"It's the phoniness and this cruelty. Donald is cruel," she said in recordings made public by Mary Trump.

Those absences are not surprising but Kusher's has raised eyebrows.

"He may have lost his star," said scholar Panagopoulous.

Still, in a White House that has seen the departure of many top members since 2017, the omnipresence of the president's family members at the convention suggests "when it comes to people that can sell him to the American people as someone worthy of being reelected... perhaps he can only really trust members of his own family," said Katherine Jellison, a historian at Ohio University.

She recalled that Trump's family has always been closely linked to his business: "Trump branding is always what the Trump family has been about," Jellison said.

But never in recent American history, she said, has a president's family played such a preeminent role.

The Kennedys present the closest parallel, she said, but in contrast with Trump, president John F. Kennedy "didn't want to keep reminding people of those family members' influence."

Are the Trumps going too far in the opposite direction?

"It is up to the American voters to decide," said Panagopoulos.