It was laugh-out-loud funny, Donald Trump's apparent credulousness at the way NAFTA renegotiations unofficially began a few weeks ago.

But the straight-out-of-Veep sequence of events – the U.S. President threatening to tear up the agreement altogether, his own administration helping orchestrate calls from his Canadian and Mexican counterparts to persuade him otherwise, the President then promptly climbing down while obliviously explaining the remarkable coincidence of those two calls happening almost simultaneously – was less amusing to those directly involved.

Because on the Canadian side, at least, the way it publicly played out underscored the precariousness of what might be the single most valuable relationship in this country's current cross-border dealings: the one between Donald Trump's son-in-law, Jared Kushner, and Justin Trudeau's chief of staff, Katie Telford.

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It was Mr. Kushner, The Canadian Press reported a couple of weeks after the fact, who set up the call from Mr. Trudeau. On both sides of the border, the inference being that it was a sudden intervention by the relatively free-trade-friendly Mr. Kushner, meant to thwart more protectionist voices within the White House.

But while acknowledging that Mr. Kushner was indeed involved, sources in and around the Prime Minister's Office (Ms. Telford not among them) suggest that the call was neither out of the blue nor particularly dramatic in and of itself.

The reality, those sources say, is that Mr. Kushner and Ms. Telford have been in very frequent phone contact – perhaps more so than any other high-ranking members of either administration.

Their relationship took root prior to Mr. Trump's inauguration in January, when Mr. Trudeau's government began an aggressive outreach campaign aimed at any and all with influence on the incoming president. That included pairing Mr. Trudeau's top two staffers with the two most powerful members (by Ottawa's reading) of Mr. Trump's inner circle. Gerald Butts, Mr. Trudeau's principal secretary, got chief strategist Steve Bannon; Ms. Telford got Mr. Kushner.

While Mr. Butts and Mr. Bannon have also kept in touch, Ms. Telford and Mr. Kushner are said to have gotten on especially swimmingly, developing an easy rapport while comparing notes and sharing ideas – among them the launch, during Mr. Trudeau's first visit with Mr. Trump, of a joint council to advance female entrepreneurs involving Mr. Kushner's wife, Ivanka Trump.

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As Mr. Trudeau's relationship with Mr. Trump moves past such largely symbolic gestures to the nitty-gritty of enormously consequential negotiations around changing the continental free-trade agreement, Ottawa could not have wished for a more opportune person in the White House with whom to have an open line.

Mr. Kushner, who at times appears to be functioning as a de facto secretary of state and at others as an all-purpose troubleshooter, does not have an easily defined role. But in an administration in which aides are constantly competing against each other for the attention of a volatile and erratic President, while seeing their influence wax and wane on a daily basis, Mr. Kushner seems to have the President's ear more consistently than anyone else.

Helping explain both his chumminess with the Prime Minister's Office and why it matters, Mr. Kushner is considered to be, alongside National Economic Council director Gary Cohn, on the relatively internationalist side of an ongoing White House fight over economic policy, pitted against the likes of Mr. Bannon and trade adviser Peter Navarro. (The latter pair reportedly drafted an executive order that would have initiated withdrawal from NAFTA, before the calls from Canada and Mexico came in.)

So beyond any immediate benefit derived from dealing with him, there is obvious Canadian upside if Ms. Telford is providing the 36-year-old real estate investor – who has no previous government experience – with advice or perspective that might help him win internal debates.

But it's that stake in Mr. Kushner's future, along with the need to maintain his trust, that made Canadian officials uneasy about how his role in the NAFTA calls to Mr. Trump became public.

It's perilous for anyone serving an "America First" President who sees trade as a zero-sum game to risk being seen as cozy with a trade partner, let alone doing its bidding. And it's probably even more dangerous, given that President's personal insecurities, to take a chance of setting him up for embarrassment, as when Mr. Trump credulously bragged about Mr. Trudeau and Mexico's Enrique Pena Nieto calling him out of the blue.

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In a White House in which warring factions scramble to put media stories that help their cause in front of a President addicted to his own coverage, it's not hard to imagine some of the U.S. accounts of how this episode played out – Vanity Fair snickering about "the Justin-Jared team" putting sense into "Trump's Twitter-addled brain," or Breitbart describing "globalist" intervention – making its way onto Mr. Trump's desk.

Fortunately, from Ottawa's perspective, Mr. Trump has bigger problems to worry about at the moment – scandals about Russian election interference and inappropriate sharing of U.S. intelligence and firing an FBI director. There is no indication that the details of a trade call or two have impacted his relationship with Mr. Kushner, or Mr. Kushner's relationship with Canada.

But even if Mr. Kushner has more rope than anyone else who advises Mr. Trump, that rope is presumably not infinite. Among Canada's many challenges in navigating the White House's palace intrigue, as NAFTA talks heat up, will be to wield its relationships effectively enough to get what it wants, and discreetly enough not to compromise them.

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