Our journey ended where it began, in a bar in New York’s East Village, sharing a bottle of wine with our old friend Martha Fishkin.
“Oh my god, you guys,” she squealed. “I can’t believe you did it. All those miles, all those states, you must be exhausted ... have another glass of wine.”
Ian, the bar manager, a handsome, urbane man from Aberdeen, stopped by. Astonishingly, he remembered us from our first visit in May, but I don’t suppose he gets many fellow Scots dropping in for a drink before setting off around the country in an old campervan.
“You will be looking forward to going home,” he stated, clearly without fear of contradiction.
“Yes,” I said quickly. Then stopped, “well, actually I could happily stay here, in this city.”
He laughed, “But Scotland is so beautiful,” and went off to tend to a birthday party that had just spilled into the bar.
Scotland is beautiful. Heartbreakingly so. Tomorrow morning when I wake up in my own bed, and look out at Arthur’s Seat on the horizon, beyond Fisherrow harbour, I will be happy that I am home. But it is not New York.
This is the city where, reportedly, 800 languages are spoken. The city where brilliant ideas are born every New York minute, and just as quickly discarded for the next big thing.
The city where people from across the globe come, eager to make a new life, to inhale the forceful, creative human energy that powers this place.
Andrew Warhol was a diffident 21-year-old art school graduate when he left Pittsburgh to come to New York in 1949.
He died 37 years later as Andy Warhol, the quintessential New York artist, who won fame and made a fortune out of painting soup cans and holding parties.
But there was much more to Warhol than careful studies of Brillo pads and gaudy portraits of Marilyn Monroe.
As you wander round the major retrospective of his work, ‘From A to B, and Back Again’, which has just opened in the Whitney Museum of Art, his genius unfolds before you.
He helped create the 21st century, despite dying in 1986. His perfectly square studies of the rich and famous are his Instagram feed. The grainy, black and white home movies he made in his New York Factory are his YouTube channel.
His most famous expression, “In the future, everyone will be world-famous for 15 minutes” anticipated the social media age where a single tweet can change the world.
Warhol embodied the spirit of New York, its creative force, sometimes dangerous, always exciting. There is simply nowhere in the world quite like it.
And there is nowhere in the United States of America quite like it either. Los Angeles is a series of suburbs, New Orleans a musical village. Atlanta has a progressive energy that suggests a bright future. San Francisco is designing the future.
But no other city has the same sense of endless possibility, of waking up in the morning, knowing that by the cocktail hour something interesting, good or bad, will have happened, at least once.
Until now that is, because thanks to Donald Trump, a New Yorker born and bred, the rest of the country is learning what it is like to live in the city that never sleeps.
No President, living or dead, has created as much news as Trump. Every day brings a new set of headlines, a new outrage. Sometimes two or three in one day. Like a long weekend in Manhattan, it’s exhilarating. It’s also exhausting.
In the last few days, General Motors has announced plans to lay off 15,000 workers and close five plants, in part because of Trump’s steel tariffs.
Trump’s border agents lobbed tear gas at toddlers in nappies as their parents tried to enter the United States in search of a better life.
The special investigation into the Trump campaign and possible collusion with Russia erupted amid accusations that the president’s lawyers have been conspiring with his former campaign manager’s legal team to obstruct justice.
And Melania Trump unveiled a surreal display of blood red Christmas trees that has transformed the White House into the set of the Handmaid’s Tale.
“The USA is booming!” tweeted Trump.
“We will CLOSE our Southern Border,” he warned.
“When will this illegal Joseph McCarthy style Witch Hunt, one that has shattered so many innocent lives, ever end – or will it just go on forever?” he countered.
“Those trees are very creepy,” said everyone on Twitter, though I suspect Warhol would have approved of Melania’s bold choice.
Warhol and Trump knew each other in the 1980s. Of course they did. This is New York. Trump commissioned Warhol to do a portrait of Trump Tower, but the initial drawings were rejected, as Warhol recalled later in his diary.
“I did eight. In black and grey and silver which I thought would be so chic for the lobby. But it was a mistake to do so many, I think it confused them.
“Mr Trump was very upset that it wasn’t color-coordinated ... I think Trump’s sort of cheap, though, I get that feeling.”
But not even Warhol, the genius who foretold the digital age, could have anticipated that one day, the “cheap” property developer would be President of the United States of America.
As we prepare to leave New York, another big news story explodes.
Michael Cohen, once Trump’s personal lawyer, pled guilty to lying to Congress about Trump’s real estate deals with Russia during the 2016 election campaign.
“He’s weak. He’s lying,” boomed Trump as he headed off to the G20 in Buenos Aries.
“He’s telling the truth,” asserted the special investigation team, after Robert Mueller offered Cohen a deal in exchange for his co-operation.
And as Trump’s plane took off, news emerged that Deutsche Bank – the only major financial institution willing to lend to the Trump Organisation in recent years – was raided as part of a money laundering investigation.
The 15-minute Presidency might just be rushing towards its inevitable, messy end.
It’s a tale that could only have emerged from this city, where everything – even its high crimes and misdemeanours – is larger than life and more astonishing than any pop artist could ever imagine.