In 1849 a Scottish traveller to the United States, Alex Mackay, observed that "English names are plentiful around you, and many objects within view have an English look about them. Yet, when the Englishman steps ashore, it is on a foreign, though a friendly land."
This was an insight of fundamental importance, which we Brits have to learn and learn again. I love America. But it is foreign, more foreign than a common language, shared history and the 'special relationship' would suggest. How many British businesses have failed in the US for believing that it was Britain writ large?
When I first went to live in the US in 1988, I had my Alex Mackay moment. I was doing a sabbatical at Harvard and, with my first wife and young children, lived in a house just off campus in a street with an impeccably English-sounding name; Grey Gardens East.
At first blush it all looked and felt so English - after all this was New England. My kids went to a school with a name straight out of Charles Dickens: Buckingham, Brown and Nichols.
But it was the school that first made me realise that this was a society which marched to a different beat from dear old Blighty. The Parent-Teacher Association was restlessly active and demanding of parents. Fund-raising was direct and to the point. Every year the school publicly ranked donors in descending order of generosity. At suppers and barbecues with other parents I rapidly found out that conversations about religion, crime and punishment, abortion, patriotism, politics could start from wholly different first principles.
After a few months I went on a lecture tour to towns in Oklahoma, Texas and Louisiana. There, outside the rarefied air of the Harvard bubble, these differences were even more sharply drawn.
When addressing an audience in Tulsa, Oklahoma, I was introduced thus: "Christopher Meyer has come to talk to us from Harvard, but we won't hold that against him!" Everyone laughed uproariously. But, there was a serious undertone.
All this comes to mind, observing the primary election contests to nominate the Democratic and Republican candidates for the US presidency. Last week the Iowa caucuses, this week the New Hampshire primary, each following rules and procedures quite different from the other.
So it continues state by state, until a victor emerges, bloody but unbowed, from one of the universe's most punishing electoral processes. Obama is, of course, a shoo-in for the Democratic nomination. But uncertainty hangs over the outcome of the Republican primaries, where Mitt Romney, the wealthy ex-governor of Massachusetts, is still an unconvincing favourite.
Politics provides one of the most vivid and telling measures of how wide the Atlantic really is. It is not just that the point of gravity in America is so much further to the right, such that David Cameron would be considered by many Americans as 'socialistic' just for his support of the National Health Service. It is that ideas and beliefs that would be thought daft in Britain are part of mainstream discourse in the US.
Look at the Republican field. Mitt Romney - a centrist politician who has always looked uncomfortable trying to appeal to his party's right - was once a Mormon missionary in France, as his father had been in Glasgow. This meant, among other things, trying to convince people that an angel of God, called Moroni, had revealed in 1823 to one, Joseph Smith, that a collection of ancient writings, engraved in gold, had been buried in Wayne County, New York.
Yet Romney is the only Republican contender currently considered to have broad enough electoral appeal to attract independents and to stand a chance of defeating Obama.
It could be the kiss of death to his campaign to say too loudly that, Mormonism aside, he is also the only candidate in the Republican field with whom Europeans would feel remotely comfortable - except perhaps for Jon Huntsman, another Mormon and moderate. Compared to those snapping at his heels, like the uber-rightwinger, Rick Santorum, and the eccentrically libertarian, Ron Paul, he looks positively normal. I once met Romney in Salt Lake City, the capital of the Mormon state of Utah, and found him a classic mainstream Republican of the old school.
A lot of this is for the anoraks and nerds, like myself, who follow every twist and turn of American politics. But, in the large picture, it is God who makes the big difference between the two sides of the Atlantic. British politics, like most European politics, is irredeemably secular, as Santorum has disapprovingly noted. God does not even get a walk-on part in our elections. In America he is centre-stage, wherever you place yourself in the political spectrum, to be invoked as much by Barack Obama as Texas Governor Rick Perry, who has apparently been told by God to stay in the Republican primary race.
So, if the politics of our most important ally and partner, the USA, is suffused with religiosity, let us not automatically jump to the worst conclusions when Islamist parties do well in elections unleashed by the Arab Spring.