Nic Robertson is CNN's international diplomatic editor. The opinions in this article belong to the author.

(CNN) As with any tragedy there is shock -- this is what America's allies are experiencing right now. Other emotions will follow: anger, resentment, and the desire for retribution likely among them.

The tragedy for America's allies is that 70 years of mutually profitable, security-enhancing relations are coming apart.

The shock is worse because the attacker causing the rift is on the inside. Even before he arrived at the G7 meeting, President Donald Trump was lobbing diplomatic grenades. Canada, France, Germany, Britain, Japan and Italy should have seen it coming.

In the days prior to the meeting in Canada, Trump, the kingpin in the alliance, had been ratcheting up increasingly caustic rhetoric over trade tariffs. And US allies were pushing back.

Then moments before leaving Washington for Quebec he called for the G7 to re-admit Russia , making it a G8 again.

It was an intentional uninvited distraction -- an increasingly frequent hallmark of Trump's abrasive diplomacy that takes time from more pressing issues.

Russia's participation in the gathering was never an intended focus on the agenda. The country was expelled four years ago for invading Ukraine and annexing Crimea.

Trump was telegraphing his combative strategy even before landing in Canada -- and further signals came in his late arrival, failure to show up on time for some meetings and early departure.

This photograph taken mid-gathering speaks volumes as an indication of what was said behind closed doors.

Both British Prime Minister Theresa May and French President Emmanuel Macron talked of difficult conversations, but pointed to the joint communique, a list of agreements, to be signed by all. In the words of Macron, it "marks a collective desire to stabilize things."

After leaving the meeting early, Trump tweeted that he was reneging on signing the communique and blasted Canada's Prime Minister Justin Trudeau. It was this reversal that spoke loudest of all, amplifying his already abundant disdain for allies.

There is now, among those allies, a bitter aftertaste. Questions that were rarely asked previously will now surface: "How did we not see this coming?" "For how long have we gone unappreciated?"

Now America's allies are staring down the twin barrels of estrangement and separation.

We are not there yet, but when one partner acts out of character, it will lead to questions among the others. The G7 fiasco has become just such a catalyst. Troubles that have been brewing have been brought to the surface with nowhere to hide.

It has become accepted that this is Trump's style: Throw the old order up in the air and create new structures from the chaos. Just before the G7 summit, Britain's Foreign Secretary Boris Johnson, was recorded saying , "I have become more and more convinced that there is method in his madness."

Referring to how Trump might handle Brexit, he said, "He'd go in bloody hard ... There'd be all sorts of breakdowns, all sorts of chaos. Everyone would think he'd gone mad. But, actually, you might get somewhere."

Inside the G7, according to his own tweet, Trump hit it off with Italy's new populist Prime Minister Giuseppe Conte. But neither Johnson nor Conte are in the mainstream of his allies.

So what could the new post-G7 order look like, absent swift rapprochement?

In the short term, an escalating trade war. If nothing changes, maybe a Europe cast off from the US, where regional energy and security concerns become their own preserve.

A future where Russia feels less caged by its fears of a mobile democratic curtain and China, unbridled by a united alliance opposing its expansionism, loosens its own fetters and engages in increasingly footloose foreign adventures.

But none of this need be. The question facing America's allies now: Is Trump America?

Regardless of who is in office, is this what we have to contend with?

Republican Sen. John McCain and former FBI chief James Comey have been quick to say no.

The reality facing G7 allies though is one of its own choosing. America is isolating itself, as Trump replaces traditional diplomacy with bullying, backed up by an army of surrogates.

None of that is an easy sell for the allies, which could mean problems for Trump in the future.

Allies are allies because, when you need them, they are there. They are made pliable through the stroking of their egos, not by rubbing them the wrong way.

But no leader at the G7 acts alone. They can only back Trump when they have the political capital at home to do it.

And on that front Trump is crimping his own power.

Macron tried warming his electorate to Trump but that bromance blew up over trade tariffs several weeks ago.

Britain's May is bracing for large street protests next month when Trump comes to the UK to meet her and the Queen.

She has already been criticized for her closeness to Trump and, given her weakened political standing, will be all too aware of how former British Prime Minister Tony Blair's political career was truncated by his support for President George W. Bush in Iraq.

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Last year more than 1.8 million Brits signed a petition demanding Trump be denied a Royal audience.

In a post-Quebec world, where allies answer Trump's claims about trade imbalances, disappointment and disillusionment in America is going to reach electorates fast.

Division begets more of the same.

The allies' relationships with America are already reshaping. Nothing is irreversible yet, but Trump is accelerating towards a point of no easy return.