Pondering an earlier run for the presidency five years ago, Trump revealed his supposed doubts (“the whole thing is very strange”) about where Obama had been born, a useful marker for a campaign that never was, a useful marker for the campaign that now is. According to at least one poll, a majority of Trump supporters believe Obama was born outside the US. The Donald, salesman, reality TV star and showman, understands his audience.

And he knows what his audience thinks about immigration. If there’s one issue that divides the GOP’s leadership (pro-immigration) from much of its rank-and-file (not so much), it’s that. The Republican leadership’s position is the product of ancient economic orthodoxies (the more people the merrier), Ellis Island romanticism, hard-nosed calculation (corporate donors appreciate the cheap labour) and the doomed hope that it will endear the GOP to Latino voters. It is a stance that was reflected, to varying degrees, by all the professional politicians running for the Republican nomination, leaving a gap in the political market that Trump — the businessman — filled.

Trump made immigration a key focus of the speech in which he declared his candidacy last June (that “great, great wall”) and, no blow too low, he linked it to crime (“When Mexico sends its people, they’re not sending their best . . . They’re bringing crime. They’re rapists.”) saying aloud what many of his potential supporters suspect. In all probability it was the immigration issue which, more than anything else, powered the dramatic acceleration in Trump’s support in the weeks that followed his entry into the race, an acceleration that transformed him from joke to contender.

Trump is also trying to appeal to the same “left behind” section of the electorate — and not just them — with his pledges to protect social security (pensions) and Medicare (health care for the over-65s). And he wants those manufacturing jobs back. Asserting that America has been hard done by — an argument that will resonate with those who feel themselves hard done by — he claims to be in favour of free trade, but not “stupid trade”. That’s a concept that, like so much of his programme, takes some parsing, but should be read as a promise that Donald Trump, famed dealmaker and (best-selling!) author of The Art of the Deal, will be able to cut better trade deals than the saps that have been handling these matters up to now. He is threatening to “break” Nafta and has talked about a 45 per cent tariff on imports of Chinese goods. Somewhere Smoot and Hawley are smirking.

This theme of an exploited America runs through Trump’s sometimes alarming foreign policy musings, notably his (not entirely unjustified) complaints about US allies (including some in “obsolete” Nato) who don’t pull their weight. Beneath the wild talk, there’s something more substantial, an appeal to a more self-interested nationalism, and with it the implication that the messy international interventions of the past can be avoided (“we cannot be the policeman of the world”), an idea likely to play well in a country exhausted by years of conflict, and not least in those communities that provide the boots on the ground.