Mitt Romney's gaffe-ridden visit to Europe has been passed off with the general conclusion that this man couldn't possibly be president of the US or, at least, would be a disaster if he were. But we shouldn't be so hasty to dismiss him. It isn't that he is a better man or politician than he appeared to Europe's jaded appreciation. He may well be every bit as bad. But the foreign policy he espoused, or rather the set of prejudices he pursued, reflect precisely the assumptions of the US at large.

Like David Cameron and Tony Blair before him, this is a candidate driven by opinion polls far more than conviction. What the polls say is that the majority of Americans believe that support for Israel is the most important single tenet of US foreign policy, that Iran is the biggest single state enemy to be confronted, and that Poland, rather than Germany or France, best expresses America's beliefs on the Continent.

You can say, as every commentator has, that Romney's mis-steps mean nothing back at home, that it is the domestic economy not foreign policy which will determine the outcome of the election. It is precisely because foreign policy doesn't matter electorally but remains the area of greatest presidential freedom of action, however, that Romney's views should worry us over here. Democrats may try to make political capital out of his international competence but they are not prepared to challenge his assumptions.

To be fair to President Obama, he has at least managed to keep at bay the demands for military action against Iran or intervention in the Arab Spring. What he has not been able to do is to break out into a new and imaginative policy towards the Middle East, engagement with Iran, negotiations with North Korea or an effective alliance to Pakistan. Events in these countries have hardly made it easy for him. Congress has also been far from helpful. But then neither has Obama's preference for consensus.

President Obama's first term has at least witnessed a retreat from the excesses of President Bush's ill-fated foreign ventures. The US has withdrawn from active military engagement in Iraq and is now set on doing the same from Afghanistan. Other than this, however, it remains stuck in the past.

It is always unwise to underestimate US resilience, especially economically. In many ways, its retreat from foreign involvements should be welcomed after the disasters of Bush. But as the presidentials get under way, Britain and America's European allies need to face some stark facts. One is that US power is not only waning but is seen to be waning through much of the world. Another is that, whoever wins the forthcoming election, American policy is unlikely to regain much initiative.

It is always possible that a Republican Administration under Romney might encourage the Israelis to bomb Iran and set off a new Middle East conflagration, but in terms of what the US does itself in Afghanistan, against Iran or in the Middle East or Asia, a policy of passivity is likely to continue.

There is no appetite in America for foreign ventures (heaven be praised!) nor can Washington throw its weight around when it is so short of economic muscle itself. America is turning in on itself, and China, for all its new assertiveness, is far too self-obsessed to fill the vacuum, any more than India, Brazil or the other emerging economic powers.

Which leaves the UK precisely where? We can't go on trying to exert influence as junior partner to Washington. Even Cameron seemed to understand that at the beginning – before he was seduced by a special "rapport" with Obama and his wife.