While Donald Trump was revealing how he'll make Mexico pay for a wall along America's southern border - basically he plans to declare economic war on the USA's third largest trading partner - a travel article in the Herald reminded us what's at stake.

It was about Bunker 42, a facility 65m beneath the Kremlin that would have been the Soviet Union's command centre in the event of nuclear war.

The Cold War may be over but the transformation of Vladimir Putin into the recognisable heir to the Red Czars who ran the USSR has coincided with East-West relations relapsing into adversarial iciness. Russian bombers are probing Western air defences and its submarines probing Western sea defences. No doubt the West is doing some probing of its own.

Russia and America still have vast nuclear arsenals. We're talking about intercontinental ballistic missiles with multiple warheads that take less than 30 minutes from launch to detonation. The submarine-launched versions would take less than 15 minutes.

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Both countries have Launch on Warning (LOW) capability, maintaining nuclear missiles in a state of high alert so they can be launched in the time between a satellite-based Early Warning System (EWS) detecting incoming missiles and said missiles hitting their targets.

EWS/LOW is not foolproof. On at least three occasions the systems have detected inbound enemy missiles when there weren't any.

In 1979, a technician at the North American Aerospace Defence Command put a training tape into an operational computer causing it to announce that Soviet missiles were on their way.

In 1983, with tension at an all-time high, there was the "autumn equinox" incident: sunlight reflecting off the tops of clouds persuaded the Soviet EWS that five US missiles had been launched. On the basis that if America was going to launch a pre-emptive strike it would fire a lot more than five missiles, Lieutenant-Colonel Stanislav Petrov opted not to pass the information up the chain of command. He's sometimes referred to by war gamers and military historians as "the man who saved the world".

In 1995, the Russian EWS interpreted a Norwegian scientific rocket launch as the US engaging in a gambit called "x-ray pin down": detonating a submarine-launched warhead over enemy territory to blind its radar ahead of full-scale strike.

The Russians had been told about the Norwegian rocket but the information didn't get to the right people. The lack of activity around US missile silos persuaded the right people that it was a false alarm.

The second issue with EWS/LOW is that it gives the respective leaders about 12 minutes to press the button or wait and see if it's for real. (The alternative to LOW is RLOAD: retaliatory launch only after detonation.)

Hence the US President holds mankind's fate in his or her hands, which is why we all have a stake in this election. Notwithstanding Trump's claim that he has large and powerful hands, the rest of the world has good reason to dread the prospect of its fate in those mitts.

Trump lacks knowledge, experience, judgment, character and the humility to recognise that. In his world view, America has no friends. Its so-called allies are cynical freeloaders who want America's protection because it's cheaper than fending for themselves. The Chinese are thieves, Mexicans are rapists and Muslims are terrorists. The only foreigner he has a favourable opinion of is, revealingly, Putin, but that bromance isn't built to last.

Trump's admirers compare him to Ronald Reagan, who also scared the daylights out of the rest of the world. What they don't trumpet is that, before Reagan surprised even his closest advisers by joining Soviet leader Mikhail Gorbachev to reduce nuclear weapons, the world came as close as it has to Armageddon.

Two months after the autumn equinox incident, the American-led Nato alliance embarked on Able Archer 83, a massive military exercise that simulated conflict up to Defcon 1: nuclear war imminent. Reagan's bellicose rhetoric, his support for the so-called Star Wars initiative and the steady build-up of tension since he'd taken office, together with the realistic nature of the exercise, persuaded some in the Soviet High Command that Able Archer was an elaborate ruse concealing preparations for a pre-emptive strike.

The USSR put its entire arsenal into actual - as opposed to simulated - launch mode, one command from nuclear war.

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