After Donald Trump’s atrocious and irrational behaviour leading up to and at the Group of Seven summit, the disintegration of the liberal world order in place since the end of the Second World War and the potential for a serious international crisis no longer seem hard to imagine.

The President, unmoved by history, ignorant of facts and guided by sycophants, has not been forced to grapple with the real world nor to hear views that don’t coincide with his twisted world view, in which allies are ripping the United States off and aggressive strongmen are to be admired and accommodated.

Trump, after departing the G7 meeting early, reversed his earlier decision to sign on to the joint statement with other member nations. He no doubt was reacting to the public tongue-lashing from Canadian Prime Minister Justin Trudeau, who told the media: “I highlighted directly to the President that Canadians did not take it lightly that the United States has moved forward with significant tariffs on our steel and aluminium industry.”

Trudeau continued by declaring that the Trump Administration’s decision to invoke “national security” to justify tariffs was “insulting” given Canada’s alliance with the United States in multiple wars. As Trudeau put it, “Canadians, we’re polite, we’re reasonable, but we also will not be pushed around.”

Trump can never tolerate criticism, let alone such public and direct criticism, so he accused Trudeau of making “false statements” and reneged on the decision to sign the joint communique.

Trump demonstrated once again that he is erratic and untrustworthy — with his own allies. The contrast between his antagonistic relationship with democratic allies and his never saying a bad word about Russia defies explanation, unless one is to buy into the theory that he is indebted in some fashion to Russian President Vladimir Putin, whose campaign to interfere in the US elections helped to land Trump in the White House.

Even before this diplomatic disaster, Trump was already grumbling about his failure to get the allies to capitulate.

The Washington Post’s Damian Paletta and Anne Gearan report:

President Trump told foreign leaders at the Group of Seven summit that they must dramatically reduce trade barriers with the United States or they would risk losing access to the world’s largest economy, delivering his most defiant trade threat yet to his counterparts from around the globe.

Trump, in a news conference before leaving for Singapore, described private conversations he held over two days with the leaders of Britain, France, Germany, Italy, Japan and Canada. He said he pushed them to consider removing every single tariff or trade barrier on American goods, and in return he would do the same. But if steps aren’t taken, he said, the penalties would be severe.

“We’re the piggy bank that everybody is robbing,” Trump said. “And that ends.”

I have no idea what he is talking about. Our allies are not stealing anything. It is far from clear what, if anything, would satisfy him. If — and it is a big if — Trump is serious about erecting barriers to US markets, we are looking at a full-blown trade war with our closest allies and trading partners, along with the trade wars with China and Mexico. All this would redound to the benefit of exactly one country, Russia. A worldwide recession would not be hard to imagine.

Trump becomes irrational and unhinged when contradicted, and given the degree of contradiction permitted within his inner circle, none, it must be unnerving indeed to discover that our allies view him with disdain if not contempt. Arriving late and leaving early from the G7 gathering, Trump played the petulant child, trying so very hard to say that he didn’t want to be part of their group anyway — so there. Worse still, his disturbing invitation for Russia, the United States’ most worrisome foe, to join the G7 suggests he really cannot tell who is a friend and who is an enemy.

Trump’s Republican enablers, who ridiculed liberal Democrats for coddling dictators and ignoring allies — ah, the good old days when they groused, inaccurately, about the return of a Churchill bust — should see what their grovelling has wrought. They now back a president who does not put America or the West first. A Manchurian candidate could not show greater fealty to Russia nor more diligence in helping Russia to pursue its goals.

Senate Majority Leader Mitch McConnell, who refuses to consider reclaiming Congress’s role in trade, will see the consequences that flow from his and his fellow Republicans’ neglect of their constitutional obligations. Republicans have rejected their obligation to restrain an unfit executive and lessen the damage by reasserting Congress’s rightful power in areas such as trade. They are now Trump’s facilitators in his apparent desire to blow up the international world order — the world order that America helped to create and has always led. In that sense, McConnell, too, is helping, wittingly or not, to make Russia great again.

Last week, McConnell bragged that the past 16 months have been the best he has ever seen for conservatism. Unless “conservatism” means the anti-liberal regimes in Europe and Russia, that evaluation is daft. Starting trade wars, coddling enemies, inflating the debt, tolerating widespread corruption and fanning despicable, racial animus make for “success” in conservatives’ minds?

No wonder many former Republicans cannot abide the present GOP. These political outcasts have for decades been against every one of the things I just listed; the GOP now accepts and even celebrates every one of them. The question is not why former Republicans have left the party, but what purpose the party serves beyond sustaining Trump.

As Trump is poised to meet with North Korean dictator Kim Jong Un, he declares he will know within a minute whether the meeting will be a success. Here is a man declaring his gullibility and waiting to be snookered with a few smiles, some stomach-turning flattery and many empty promises from a calculating adversary. Trump seems not to know that the first meeting between the US president and the dictator of North Korea is not an amazing achievement for the United States; it’s a huge win for Pyongyang.

In the case of the Singapore summit, we really do see a zero-sum equation. Trump, for fear of failing, seems to have defined “success” down to a photo op, thereby giving a massive victory to Kim, who obtains legitimacy and reduces, if not eliminates, any real risk of military action against his regime.

Kim will do what North Korea has done again and again: speak nice words, pull the United States into fruitless discussions and give up nothing of consequence. The empty gesture of formally ending a war that has been over for 65 years achieves nothing for the United States but will burnish Kim’s image.

The notion that real denuclearisation is even possible needs to be rethought. How could an entirely closed regime, replete with secret labour camps and a substantial military, ever allow inspectors to rove the entire country to determine what it has and what, if anything, it is giving up?

How could Kim give up the jewel of his regime, the very thing that got him a summit with the world’s only superpower?

Getting “investment” or economic aid from the West likely sounds like colonialism redux to the North Korean regime. Taking “help” from the West would be inviting the fox into the henhouse from their perspective. Surely someone in the Trump Administration understands this, right? Where is national security adviser John Bolton when you need him?

Trump is now so desperate to show he’s “right” — a master negotiator who breaks every precedent — that it is becoming more and more likely the summit will deliver plenty of glad-handing but no concrete moves towards denuclearisation. In that respect, Trump is exactly like every other American president who got pulled into a process whose end result is North Korea’s continuing status as a nuclear power. The main difference is that none of Trump’s predecessors were dim-witted enough to give the ghoulish dictator of North Korea a public-relations triumph.

Oh, and they managed not to get into fights with Canada.

• Jennifer Rubin writes the Right Turn blog for The Washington Post, offering reported opinion from a centre-right perspective