Even for a White House and media whose relationship has plumbed the depths of mutual animosity, the fiery exchanges last week between President Donald Trump’s senior policy adviser, Stephen Miller, and CNN’s Jim Acosta took some beating.

During a televised briefing, the two men traded barbs about the president’s new proposed legislation to halve immigration. As Mr Acosta accused the administration of betraying the spirit of the words which adorn the Statute of Liberty — “Give me your tired, your poor, your huddled masses yearning to breathe free” — Mr Miller charged the CNN anchor with “cosmopolitan bias”.

That Mr Miller should have chosen an epithet which, as the journalist Jeff Greenfield noted, has its roots in Soviet antisemitism and is now frequently deployed by the radical right to impugn the patriotism of their opponents, did not go unnoticed. Nor did the fact that Mr Miller’s riposte to Mr Acosta, that Emma Lazarus’s words were added 17 years after Lady Liberty’s dedication, rather ignored the fact that she originally wrote the New Colossus in 1892 in the wake of the onset of the Tsarist pogroms which ushered in a wave of Jewish immigration to the United States.

While Mr Trump will no doubt have revelled in his senior aide’s ferocious defence of a key administration priority, there was nothing staged about Mr Miller’s performance. Unlike other senior Jews in the president’s inner-circle — Mr Trump’s daughter, Ivanka, son-in-law Jared Kushner and chief economic adviser Gary Cohn — Mr Miller has no past association with liberal causes or the Democratic party. Instead, the 31-year-old — who wrote Mr Trump’s infamous “American carnage” inaugural address, was a prime mover behind January’s travel ban and has helped craft the new bill to cut immigration — is a true believer in the nationalist populism which many credit for last November’s shock election result.

That Mr Trump is reported to refer to Mr Miller and Steve Bannon as “my two Steves” underlines the ideological synergy between the two men.

But while Mr Bannon hails from a working-class Irish home, Mr Miller’s parents were Democrat-voting liberal Jews from California. As a precocious teenager, their son became an avid conservative, converted by reading an anti-gun control screed by the chief executive of the National Rifle Association, Wayne LaPierre. His youthful diatribes against multiculturalism, the alleged unwillingness of his school’s Latino pupils to speak English and the supposed lack of patriotism of his teachers soon made Mr Miller a favourite guest on conservative talk shows. Adopting the role of campus provocateur at university, he caught the eye of David Horowitz, the one-time left-wing journalist who later became a hardline conservative.

On Mr Horowitz’s recommendation, Mr Miller was employed by Alabama’s right-wing Senator Jeff Sessions. Together, the pair led the fight to scupper a bipartisan push for immigration reform during President Barack Obama’s second term.

Although the president has now soured on the man he went on to appoint as Attorney General, Mr Sessions was one of the few senior Republicans to support Mr Trump during the primaries. As Mr Sessions’ communications director, Mr Miller had already forged close links with Mr Bannon’s alt right website, Breitbart News, which regarded his boss as something of a political hero.

Mr Trump would soon tap Mr Miller to join his campaign. The candidate’s regard for his young staffer was such that he frequently became Mr Trump’s warm-up act at rallies: delivering ominous warnings about criminal immigrants threatening the US way of life.

Mr Miller’s appeal to Mr Trump is obvious. His dogged loyalty is said to involve never contradicting the president and providing news clippings to back-up his beliefs.

Mr Miller’s deep-seated hostility to immigration is, perhaps, more surprising. His great-grandfather arrived from Belarus with $8 in 1908. The family’s story — the Glossers acquired a string of stores and became known as “Pennsylvania’s first family of retail” — epitomises the American Dream. But then again, as Rob Eshman, editor-in-chief of the Jewish Journal of Greater Los Angeles wrote last summer: “By becoming Trump’s anti-immigrant avatar, Miller demonstrates that in America, truly anything is possible. The great-grandson of a desperate refugee can grow up to shill for the demagogue bent on keeping desperate refugees out.”