The eldest son has done most damage. US President Donald Trump was pitched into the biggest crisis of his controversy-plagued White House tenure last week. His namesake, Donald Trump Jr, was primarily responsible.

As the multi-pronged investigations into alleged Russian meddling in last year's presidential election have ground on, the president's allies had constructed their defence on one foundation.

Yes, Vladimir Putin's acolytes might well have interfered, they allowed. But there was no communication or collusion between the Russians and the Trump campaign team.

The Trump case may have been holed below the waterline last week, when Trump Jr released a June 2016 email chain between himself and a British music publicist acting as an intermediary.

In the emails, the publicist, Rob Goldstone, reaches out to the son of the future president, suggesting that a Russian lawyer could share damaging information about Hillary Clinton, whom Trump Sr was due to face in a general election which was then five months away.

Crucially, Goldstone claims that this is part of an orchestrated effort.

"This is obviously very high level and sensitive information but is part of Russia and its government's support for Mr Trump," he writes.

Trump Jr, replying almost immediately, enthuses: "If it's what you say, I love it especially later in the summer" - an apparent reference to the possibility that the information could be put to best use as the general election campaign against Clinton ramped up.

Trump Jr published the email chain on his Twitter account Tuesday morning, claiming in an accompanying statement that he was doing so "in order to be totally transparent".

That rationale was met with a large dose of scepticism. The New York Times already had the emails, it soon emerged, and was about to reveal them when Trump Jr volunteered them instead.

In the furore that followed, the president's critics screamed for blood. Even a moderate Democrat such as Virginia senator Tim Kaine - Clinton's vice-presidential running mate last year - raised the prospect of "treason".

Investigators working with Robert Mueller, the former FBI head who is now probing the Russian matter in his new role as a special counsel, will be looking at the emails, CNN reported.

Among Republicans who are openly critical of Trump - a significant and growing constituency - the outrage was clear.

"It is pretty astonishing that top people in the Trump campaign would be not just willing but eager to meet with a hostile foreign power to receive dirt on an opponent in a presidential campaign," said Peter Wehner, who worked in the White House administrations of the last three Republican presidents before Trump.

The president is standing by his son - so far. In a statement read by spokeswoman Sarah Huckabee Sanders to reporters in the White House briefing room last week, Trump called Donald Jr "a high-quality person", adding, "I applaud his transparency."

After Trump Jr gave his first TV interview about the controversy - to a sympathetic host in the shape of Sean Hannity of Fox News Channel - the president took to his favourite medium of Twitter.

"My son Donald did a good job last night," he wrote. "He was open, transparent and innocent. This is the greatest witch hunt in political history. Sad!"

Others were not so forgiving. Social media lit up with comparisons of Trump Jr to Fredo, the hapless son of mafia don Vito Corleone in The Godfather movies.

Others recirculated one of Trump Jr's most inglorious moments - a photo of him, taken on a hunting trip in Africa in younger days, holding aloft the severed tail of an elephant.

In the photo, the future president's son wears a half-smile and what appears to be an ammunition belt. To critics of both father and son, it is emblematic of much that they find objectionable about the Trump brand - a purported mix of cruelty, wealth and entitlement.

But Donald Trump's relationship with his eldest son, and his other children, has always been more complicated than that.

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Trump's eldest three children, Donald Jr, Ivanka and Eric, are the offspring of his first marriage, to Ivana Trump, a one-time competitive skier and model. The union fell asunder in part because Trump had an affair with the woman who would become his second wife, Marla Maples.

With Maples, he had one child, a daughter who is now 23 years old. She is named Tiffany, after the famous jewellery store next door to the businessman's signature skyscraper, Trump Tower. The name may be ostentatious but Tiffany Trump took a low profile during his election campaign and continues to do so.

Trump's current marriage, to former model Melania, has also produced one child, 11-year-old Barron, who moved to the White House with his mother only last month - and whose privacy the news media has largely respected.

Trump's children from his first marriage have talked in the past about the difficulties they experienced in coping with their parents' divorce.

The lurid nature of the break-up hardly helped. One infamous example came when tabloid New York Post splashed Maples's claim that her amorous activities with Trump amounted to the "best sex I've ever had" across its front page.

Donald Jr, who was about 12 years old at the time, would recall years later to a New York Magazine interviewer: "You don't even know what that means. At that age, kids are naturally cruel. Your private life becomes very public, and I didn't have anything to do with it: my parents did."

Donald Jr stopped speaking to his father for about a year at the time of the divorce. In the same New York Magazine interview, he expressed some degree of regret for blaming his father for the collapse of the marriage.

"That's, perhaps, not actually what it was," he said. "But when you're living with your mother, it's easy to be manipulated. You get a one-sided perspective."

Ivanka sought to put a more positive gloss on the divorce. "It also made us closer to dad," she asserted. "We didn't take his presence for granted anymore."

Even setting aside the turmoil of the Donald-Ivana split, the children's early memories suggest a distance from both parents, especially their father.

Donald worked constantly. Ivana, who managed a casino complex her husband then operated in Atlantic City, had plenty of demands on her time, too.

The children were looked after in part by two Irish nannies named Dorothy and Bridget. In the summer, they often spent time with their maternal grandparents in what was then Czechoslovakia.

"It wasn't a typical 'let's go play catch in the backyard' sort of father-son relationship," Donald Jr told CNN in April 2016.

"We always went to job sites with him. We'd be in his office playing with trucks as a six-year-old while he's negotiating deals with presidents of major companies."

On the other hand, the Trump children were by most accounts less spoiled than many of their peers among Manhattan's super-wealthy.

They received allowances that were modest enough to make casual jobs appealing through their teenage years. Donald Jr at one point worked as a dock attendant at one of his father's properties, where he was paid the minimum wage and helped tie up the boats of rich visitors. Still, it was a gilded world and one which none of the children made any real effort to escape.

After university, Donald Jr spent what appears to have been a short but hedonistic period in and around Aspen, Colorado. In due course, he gave up drinking. He, Ivanka and Eric all more recently held senior roles in the Trump Organisation.

In January this year, the soon-to-be-inaugurated president announced that he had handed over control of his business to his two adult sons, saying he hoped to avoid conflicts of interest. "They're not going to discuss it with me," he told the assembled media.

But that wasn't enough to satisfy ethics watchdogs, who noted that the patriarch would still ultimately win or lose depending upon the overall performance of the business.

"Nothing short of divestiture will resolve these conflicts," said Walter Shaub, then the head of the Office of Government Ethics.

He also contended that Trump was breaking with precedents that had been in place since shortly after the Watergate scandal that forced Richard Nixon out of office in 1974. Shaub resigned from his post earlier this month. But now the spectre of alleged scandal is stalking the White House once again.

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Ivanka Trump was not named to run her father's business empire after he became president.

But that decision indicated an abundance of trust in her, not a shortage of it.

She soon moved to Washington with her husband, Jared Kushner and their three young children. The real purpose was clear - to be at her father's side.

Ivanka has long occupied a special place in the Trump hierarchy.

"Everyone in the family seems to acknowledge without overt rancour that Ivanka is the favourite," a Vanity Fair journalist wrote late last year.

At times, Trump's regard for his daughter has been expressed in terms that might generously be called idiosyncratic.

"I've said that if Ivanka weren't my daughter, perhaps I'd be dating her," he said during a 2006 TV appearance, in which he also praised her "very nice figure". She was sitting beside him at the time. She laughed and shook her head in response.

During last year's presidential campaign, the eldest daughter also defended her father's attitudes to women, which came into harsh relief when an old recording of him talking in crude and sexually aggressive terms came to light.

Ivanka and her husband are widely perceived to exert a somewhat moderating influence on President Trump. Ivanka has often stressed the needs of working women, and she and Jared are considered more friendly to the cause of LGBT rights than some other members of Trump's inner circle.

Still, the tide of Russian allegations has begun to lap at Jared Kushner's feet, too. He has an official role in the White House - senior adviser to the president - and as such was required to submit paperwork to gain the appropriate security clearance.

On the initial version of those forms, Kushner failed to disclose "dozens of contacts with foreign leaders or officials", The New York Times reported in April.

Kushner's lawyer has said the forms were submitted early in error, and that his representatives told the FBI just one day later that he would provide additional information.

Among the meetings that Kushner did not instantly mention, however, was one with the Russian ambassador to the US Sergey Kislyak and another with the top man at a Russian state-owned bank - as well, it now appears, as the meeting with the Russian lawyer that this week returned to bite Donald Trump Jr.

Kushner, Trump Jr and then campaign chairman Paul Manafort all attended that encounter.

Back in January, when Trump was turning the management of his business over to his sons, he joked that he could come back after leaving the White House and tell them, "You're fired" - the catchphrase of his hit reality TV show The Apprentice.

Donald Jr tweeted a clip of that remark, and added his own comment: "Well this could be interesting in 4 to 8 years. #nopressure."

It has taken just six months for life to get very interesting indeed for the Trump family. The pressure may only get more intense from here.

Niall Stanage is an Irish journalist and associate editor of the American political newspaper 'The Hill'

Sunday Independent