And Kim Jong-un notoriously had his half-brother Kim Jong-nam assassinated by having VX nerve agent rubbed into his face in Kuala Lumpur airport. He had his defence chief and other top officials killed at a firing range. Not content to have them shot with rifles, he had them blasted apart with anti-aircraft guns.

Third, he has been covertly conducting cyber aggression against the US and its allies, including Australia, even as he made peace overtures. The cyber research firm McAfee said that the North Korean attack, which it named Operation GhostSecret, started in March and was probing for secrets of critical infrastructure and telecommunications.

Fourth, in recent days evidence has emerged that Kim's most concrete peace gesture is incomplete and insincere. The North Koreans refused to allow expert observers to witness the supposed destruction of the Punggye-ri nuclear test site, but it did invite foreign journalists to see the event. The underground tunnels were supposedly collapsed by large detonations, rendering future nuclear testing impossible. Expert imagery analysis published on May 31 by the specialist North Korea-watching 38north.org website raises "a number of questions" on "the issue of whether the destruction of Punggye-ri is irreversible".

Frank Pabian, Joseph Bermudez and Jack Liu offer evidence that the North Koreans may have concealed one tunnel entrance, that there may be other, deeper tunnels, than the ones disclosed, and that the complex might be readily reopened for further nuclear testing. Kim, in other words, may well be hedging. They also wonder why most of the administrative buildings at the site were shown to foreign journalists and demolished, yet the main headquarters building was concealed and kept intact.

So to trust any undertaking by Kim on his country's nuclear program would be an act of faith rather than reason, hope over evidence.

And Kim is not the only rogue leader at the Singapore summit. Donald Trump has gone rogue as he breaks solemn undertakings of the US. Trump has withdrawn the US from the six-party nuclear agreement with Iran, a commitment enshrined in a UN Security Council resolution, although even his own top officials testified that Iran was honouring the deal. The agreement had seven years left to run.

This is perhaps the most troubling of all Trump's breaches and backpedals. Because it shows that he does not put priority on the containment of nuclear war. In breaking the US end of the bargain, he showed that he was prepared to put his own political convenience first.

If he's prepared to walk out on that hard-won agreement, why wouldn't he walk out on one with North Korea in the event that it became politically inconvenient?

And it is a stark example of Trump's disregard for the interests of US allies. After he announced America's withdrawal, three dismayed US allies issued a statement pledging to try to keep the Iran deal alive. “This agreement remains important for our shared security,” said Britain’s Theresa May, France’s Emmanuel Macron and Germany’s Angela Merkel.

Of course, there are many other examples of Trump disregarding US commitments. He took the US out of the TPP trade agreement, and he's begun the process of withdrawing from the Paris climate accord. He's seeking to renegotiate the NAFTA trade agreement with Canada and Mexico.

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The weekend's G-7 summit in Canada took Trumpian furniture-breaking to new extremes. He wasn't content to upset the other leaders by proposing that Russia be admitted to the group even as all its members enforce punitive sanctions on Moscow for invading a neighbour. Nor was he happy just to impose punitive US sanctions on the steel exports of some of America's key G-7 allies including Canada, Britain, Japan, Germany and France. He went further to affront and offend the other leaders. His trade adviser Peter Navarro took it into the surreal by saying that "there is a special place in hell" for Canadian Prime Minister Justin Trudeau for daring to disagree with the US President. And Trump personally delivered the coup de grace by signing a very bland G-7 communique, only to repudiate it later.

Even if Kim and Trump strike an agreement, there can be no confidence that the two leaders - or even one of them - will respect it.

The only rational course of action for a US ally, like Australia, is to heed the advice of Germany's Angela Merkel. Unable to depend on Trump's America, Europe, said Merkel last year, "must really take our fate into our own hands".

Peter Hartcher is international editor.