On Sunday evening I took my son to see Mount Rushmore. He is 13, born and raised in Britain, but with an American father and, as he put it, not enough of a British accent to impress the locals in South Dakota. Unexpected pride welled up in me when we climbed the stairs from the car park and he gasped at his first glimpse of the giant, granite-carved faces of presidents Washington, Jefferson, Lincoln and Theodore Roosevelt staring down at him. ‘Wow’ isn't a word you often hear when touring with teens.

Then we got distracted by a flat-bed trailer parked in the access road between us and the visitor centre, the walkway decorated with the 50 state flags, and the outdoor theatre facing the monument. Martial music was blaring from speakers attached to the trailer’s sides, and built up from its bed, like a float in a holiday parade, were large letters spelling out TRUMP. Beneath each letter was a list of slogans with which the president seduced millions of Americans: ‘Secure Our Borders’; ‘Drain the Swamp’; ‘Build the Wall’. Draped across the bottom was a banner reading: ‘Make America Great Again.’

We stood in stunned silence, then looked around for people suffering a similar reaction. We found a few, as well as one or two obviously afraid to react. As we watched, a pair of park rangers pulled up in their SUV. As the driver got out, I said to him: ‘I sure hope this breaks a few park rules’ – and got a cold-eyed ‘Please allow me to do my job, sir.’ In a minute the rangers were chatting away with the motley crew handing out flyers around the truck. I heard the word ‘permit’ and then we moved on, to catch the presentation in the outdoor theatre before the lights were turned on the presidential faces after sunset.

We watched a video presentation quoting Washington’s warnings against empowering the military to run civilian government. We listened to Jefferson promising full rights and the protection of the law to Native Americans. We saw Lincoln’s Emancipation Proclamation and heard Roosevelt talk about the greed of big business and the need to protect our environment. When the film ended with a rendition of ‘America The Beautiful’, the crowd joined in spontaneously.

When we walked out, past the state flags, the Trump float had been moved a few yards down the road, just past the crossing area, and the loudspeakers had been turned off. The messages we had heard just a few minutes before, of freedom, of equality, of purpose, of America’s appeal to immigrants, who were welcomed and who contributed – ideas which still inspire, even if they have never quite come to fruition – were being traduced by the men who gleefully approached us with their leaflets.

As we drove away, my son said: ‘At least we can be thankful Trump’s face will never be up there.’ ‘You watch,’ I said. ‘Next week they’ll paint his face on a giant hot air balloon, and tether it alongside George Washington.’ ‘Make America great again,’ he replied.