Buzz Aldrin has described the “magnificent desolation” of the moon. On Friday he got more desolation, but it wasn’t so magnificent.

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Aged 89, the second man on the moon hovered awkwardly at one end of the Resolute desk in the Oval Office. Michael Collins, 88, Apollo 11 command module pilot, stood at the other with his fingers pressed on the desktop. Between them sat Donald Trump, holding court not about the greatest scientific achievement in human history but trying to defend his racist attacks on a black Muslim US congresswoman.

From the sublime to the pathetic. While superficially the moon landing enables Trump, who was 23 at the time, to extol American exceptionalism and promise a flag-waving return to the moon, the unspoken truth is that he embodies the opposite of Apollo 11’s most valuable accomplishments, insights and lessons.

A day before their White House visit, Aldrin and Collins spoke at an event about “space diplomacy” at George Washington University. Collins, who went on to work for the state department, gave a lyrical description of seeing the moon up close – but said there was something even more beautiful in the opposite window: Earth.

“Out there there’s this little pea about the size of your thumbnail at arm’s length – blue, white, very shiny,” he told the audience. “You get the blue of the ocean, the white of the water and a streak of rust that we call the continents. It’s such a beautiful tiny thing, nestled in this black velvet of the rest of the universe. And that to me was the whole show.”

Suddenly, home looked very vulnerable, Collins added. “As you see this little thing, walking on it daily, is it fragile? Oh, lord, yes. Can some of those manifestations of fragility be corrected if we put our minds to it? Yes.”

Yet now America is led by a president who denies the scientific reality of the climate crisis and told journalist Piers Morgan last month: “I believe that there’s a change in weather and I think it changes both ways.” His administration is determined to gorge on the planet’s natural resources and hang the consequences.

From more than 200,000 miles away, Earth’s national borders don’t matter any more. They are artificial and arbitrary, a human construction

Collins made another striking point. From more than 200,000 miles away, Earth’s national borders don’t matter any more. They are artificial and arbitrary, a human construction. If presidents and prime ministers could enjoy such a view, the astronaut noted, they would probably struggle to identify their own countries.

It’s an argument reminiscent of astronomer Carl Sagan: “The Earth is a very small stage in a vast cosmic arena. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot.”

Yet chance has decreed that as the world celebrates the golden anniversary of the giant leap for mankind, the occupant of the White House is a man obsessed with borders and building a wall where the US meets Mexico. He has also spent the past week issuing racist tweets and basking in campaign rally chants of “Send her back!”

There was political turmoil in the US and the Vietnam war was raging, but the moon landing drew more people together, watching on TV and listening on radios, than any previous event in human history. And when the three pioneers came home, they and their wives embarked on an exhausting goodwill tour to 24 countries and 27 cities in 45 days.

Armstrong, often thought of as shy, taciturn and nerdy, turned out to be a superb ambassador, Collins recalled, not least because he had swotted up on each country in advance and was able to see things from their point of view. And what they discovered everywhere was that people did not regard it as an American achievement so much as a human one: “We did it!”

As an exercise in outreach and soft power, it was everything that Trump’s nationalist cry of “America first” is not. At Friday’s photo op, the 45th president could not resist remarking: “Tomorrow will represent 50 years from the time we planted a beautiful American flag on the moon.”

Whatever its cold war motivations, the Apollo programme began with soaring rhetoric that contrasts with Trump’s rambling word salads. Then president John F Kennedy declared in 1962: “We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills” – the last few words emphasising the need for a collective effort.

The landing itself was inherited by Richard Nixon who, from the Oval Office, made the “most historic telephone call ever” to Armstrong and Aldrin on the lunar surface, only to be later unmasked as a crook. Now his political heir occupies that office, tweeting, stoking racial tensions and appealing to humans’ darkest impulses.

It was yet another former president, Ronald Reagan, who described “mankind in his long climb from the swamp to the stars”. Half a century on from that transcendent, expansive moment, we have clearly turned around and got back to the swamp.