Portside

Any day now, monarch butterflies will begin their epic migration from Canada to Mexico. It is one of the wonders of the world: insects whose distinctive orange and black wings barely stretch four inches flying on thermal currents up to 3,000 miles in search of a warm spot to spend the winter.

The phenomenon has entranced Oscar López Rivera since his childhood days in rural Puerto Rico. If he ever gets the chance, he says, one of his great ambitions is to trace the monarchs’ route, all the way from the Canadian border, across the US great plains into northern Mexico. “The monarch is fascinating to me,” he says. “The length of their journey and what they do to survive: how can an insect so small go so far?”

That’s an achingly powerful question when you consider who is posing it. For the past 35 years, López Rivera has been unable to fly, his wings clipped. He has been held in federal institutions, for 12 of those years totally alone inside a 6ft-by-9ft concrete box from which he had no view of the sky. The last time he saw a live butterfly, let alone a monarch, was in 1981.

López Rivera is one of the US’s, and the world’s, longest-serving political prisoners. Aged 73, he has spent more than half his life behind bars. He is convicted of killing no one, of hurting no one. His crime was “seditious conspiracy” – plotting against the US state in the furtherance of Puerto Rican independence. He still believes in what he calls that “noble cause”: full sovereignty for his Caribbean birthplace that is classified as a US “territory”.

But his views on how to attain that goal have changed. Two decades ago he and his fellow Puerto Rican independence fighters renounced violence and embraced peaceful political reform. The last year in which the militant group to which he belonged committed a violent act was 1983.

Yet there he still sits in his prison cell, reading and painting, the last of his kind locked up, so venerable that other prisoners call him “El Viejo” – the Old One. It is as though he is stuck in a time-warp, trapped for ever in the headstrong 1970s, a white-haired septuagenarian forced to dress up in floral shirt, flares and platform shoes dancing to Chic. The world, and López Rivera with it, has moved on, but the US government continues to see him through the prism of a bygone age.

Unless someone intervenes to release him, he will remain in captivity until 26 June 2023, five months after his 80th birthday. Fortunately for López Rivera, there is such a person who holds the power of clemency: Barack Obama. As the US president prepares to quit the White House, he is drawing up his final pardon list, presenting the prisoner with a slender hope.

Many prominent supporters are lobbying hard for the pardon. They make for an impressive list: Archbishop Desmond Tutu; the governor of Puerto Rico, Alejandro García Padilla; the Hispanic caucus of the US Congress; former US president Jimmy Carter; Democratic presidential runner-up Bernie Sanders; and the creator of the smash Broadway musical Hamilton, Lin-Manuel Miranda, who confronted Obama about López Rivera face to face during a recent White House visit. On 9 October thousands of supporters gathered outside the White House bearing placards of the prisoner and calling on Obama to set him free, their voices projected across the mansion’s South Lawn in the hope that the president at work in the Oval Office might hear them and act accordingly.

With friends like that, isn’t López Rivera a shoo-in for release? Not according to the man himself, who remains cautious about his chances. “I do not practise wishful thinking,” he begins in perfect English, delivered with a strong Puerto Rican accent. “It’s very difficult for me to read President Obama. The way he has been treated, the obstacles he has faced in the White House, makes him a little skittish about decisions.”

What a carefully weighted remark about something as visceral as his freedom. In the course of a two-hour phone conversation (the federal prison in Terre Haute, Indiana, having refused to allow the Guardian to visit him in person) it becomes clear that this is not artifice: the professorial tone is true to the man.

López Rivera says he draws some optimism from Obama’s frequent expressions of admiration for Nelson Mandela. “He embraced Mandela as a great man, he saw that what Mandela did was important throughout the world.”

To invite comparison with Mandela may seem far-fetched for a man who in the US is relatively little known, but back home López Rivera is often cast as the “Mandela of Puerto Rico”. Mandela served 27 years in South African prisons for leading an anti-colonialist liberation struggle that deployed selective violence as a political tool; López Rivera has already served eight years longer, arguably for doing the same thing. Mandela refused to renounce violence from his prison cell; but López Rivera did so, some 20 years ago.

López Rivera was born in 1943 in San Sebastián in the north-west of Puerto Rico. His childhood was spent living in the constitutional limbo that has defined the island since it was ceded to the US by Spain in 1898. Neither a sovereign country, nor the 51st state of the union, Puerto Rico is caught betwixt and between. Its people are US citizens, hold US passports, and can be drafted into the US military as López Rivera would soon discover. Yet when it comes to voting for the US president or a representative in the US Congress, a Puerto Rican is persona non grata. Quite rich, you might think, coming from a nation such as the US, which was founded upon the anti-colonial principle of no taxation without representation.

“The only thing we are good for is to be cannon fodder,” López Rivera says in a rare display of chagrin.

Not that he had a clue about any of that when he was growing up in San Sebastián and Chicago, where his family moved when he was 14. He was just an ordinary kid for whom the concepts of self-determination or shrugging off the Yankee yoke were as alien as nuclear physics. “Before I got drafted I was a happy-go-lucky Puerto Rican. I enjoyed life. I wasn’t paying attention to anything other than me.”

Then along came Vietnam. “I arrived thinking we were bringing freedom to Vietnamese people but as soon as I hit the ground I realised that wasn’t happening. We did sweeping operations lasting 30 days, getting villagers out of their homes, moving them off the rice paddies, body-searching them.”