Mitt Romney's Gulf gaffe just a ripple in this cliffhanger of a contest

For all the rhetoric and oozing contempt, there's little to choose between them on substance

Well yes – the inhabitants of southern Iran's 1,500 miles of coastline will be astonished to learn that Syria (which doesn't even have a border with Iran) is their country's route to the sea. They don't call it the Persian Gulf for nothing.

But otherwise, Mitt Romney did what he had to do in the third and final presidential debate, the last person-to-person contact between them until one calls the other to concede the election on the night of 6 November (or maybe days – or even weeks – later, if this US election is a cliffhanger to rival 2000, as some pundits predict).

That strange concept of Middle Eastern geography was the closest the Republican challenger came to a gaffe, and nothing to match Gerald Ford's benchmark-setting blunder of 1976, when he assured Jimmy Carter in their debate that "there is no Soviet domination of Eastern Europe".

By most measures, Mr Romney "lost". But defeat was no disaster. Indeed, barring a Gerry Ford moment from Barack Obama, it would have been a miracle had he won it. Nothing prepares for the Presidency, and of all the office's learning curves, foreign policy – the one area where a US president does have a pretty free hand and where crises can explode out of the blue – is the steepest.

Mr Romney's job was not to out-argue Mr Obama, or reinvent US foreign policy in 90 minutes. It was to show war-weary American voters that he knew the basics and wouldn't be a reckless retread of George W Bush. "We can't kill our way out of this mess," he said at one of the several points at which, almost incredibly, he sounded more doveish than Mr Obama. It helps, too, that Mr Romney looks presidential (even if he seemed more nervous than in the two previous debates.)

The lesson of Boca Raton was that for all the sharp rhetoric, the mutual oozing of contempt, there's precious little to choose between them on substance.

"I agree with the President… I congratulate the President," Mr Romney said more than once.

You'd never hear words like that apropos of the domestic issues – taxes, jobs, energy policy – to which they veered back again and again.

The debate offered a few good exchanges. But it bore out a couple of self-evident truths. By and large, Mr Obama has been a safe pair of hands on foreign policy. But, short of a 9/11, foreign policy tends to be a US election sideshow, however much it matters to the rest of the world.