The Donald Trump presidency, John Oliver observed in 2017, is a marathon. “It’s painful, it’s pointless and the majority of you didn’t even agree to run it; you were just signed up by your dumbest friend,” he told viewers. “And though you’re exhausted and your whole body is screaming for you to give up and your nipples are chafing for some reason, the stakes are too high for any of us to stop.”

Activists, politicians, judges, journalists and concerned citizens are all running the race. Some have embraced the challenge and now, past the halfway point, are finding hope as they see the 2020 election on the horizon. Others have wobbled, legs buckling, consumed by the anxiety that they will never make it. Oliver, a cheerful and charming presence in a conference room at HBO’s headquarters in New York, is surely one of those runners wearing a wacky costume, pointing out the absurdity of the exercise while embodying the stamina and stoicism required to reach the finish line.

But as he prepares for a sixth season of HBO’s Last Week Tonight With John Oliver, which dissects current affairs with satire, silliness, meticulous research and a moral compass, Oliver wants viewers to know that he is neither a journalist nor an activist – and he can prove it. When I ask if he aspires to interviewing Trump, he says in an instant: “No, definitely not. There’s no point. I think he’s shallow. I don’t think there’s anything that I could get out of him. I don’t think he’s reflective in any way that is particularly useful. I think I’ll be taking up space that an actual journalist could use.

“Generally, the times when he’s most illuminating are not in interview settings. It seems like that when you read the transcripts of his junkets on Air Force One: he tends to be a little looser. Any kind of longform transcript is more illuminating, I think, than him sitting in front of someone on a camera talking. I don’t know if many interesting things have come out of that.”

Watch the trailer for the new season of Last Week Tonight.

The transcripts from Trump’s conversations with reporters on the presidential plane or at the White House are, indeed, surrealist works of art, demotic word salads matched only by Lucky’s monologue in Samuel Beckett’s play Waiting for Godot. In one episode, Oliver ran a comparison between Trump’s stream-of-consciousness ramblings and the predictive-text feature on a phone, concluding that the latter would make a more coherent president.

Such outbursts show why Trump is the gift that keeps on giving to US political comedy, from Last Week Tonight and The Daily Show (where Oliver got his big break) to The Late Show With Stephen Colbert (which found its voice and had a ratings surge after the 2016 election) and Saturday Night Live (which has given the world Alec Baldwin as Trump). All ridicule the president, a fact taken for granted by most Americans, but which would be enough to trigger censorship and arrests under many authoritarian regimes. In that sense, television’s court jesters are helping to keep the blood of democracy circulating. But when I ask if he considers himself part of the anti-Trump “resistance”, the 41-year-old bursts out laughing.

“I don’t think so, no. I think we’re only really responsible for ourselves. We try to be accountable to each other and in basic legal facts, which is why we research stuff so heavily. The press in America, of which we are obviously not a part, is under the kind of duress it has not been under for quite some time,” he says.

Brexit is a different level. You know constitutionally how Trump is going to end. But Brexit – who knows? John Oliver

“This is a confoundingly difficult presidency to cover, just because so much of what they say is not just flagrant nonsense, but also stuff that you know deep down they don’t believe, or retract the next month. It’s amazing to be in a position where you can’t really fully trust a single word that comes out of the president’s mouth, because he doesn’t believe it himself.”

According to the Washington Post, Trump made 8,158 false or misleading claims in his first two years as president. Lately, he has been fearmongering about illegal immigration to justify his demand for a border wall, even forcing a 35-day partial government shutdown and threatening another. Does Oliver believe there is method in the mendacity?

“That assumes he’s got the capacity for strategic thought,” he says. “You could definitely use the skills that he does have strategically – and sometimes, when he uses them to his benefit, it’s tempting to ascribe carefully calculated motive to it. But that’s probably not the case. He didn’t aim for the treble 20: he closed his eyes, flung some darts and one of them happened to hit it. He doesn’t even know that’s the right one to hit. He thinks the middle one is the one.”

Trump appears to go with his gut – and Rupert Murdoch’s Fox News. Analysts have found a direct correlation between the network’s talking points and Trump’s statements and tweets. “I think the thing that’s unique about this is it’s not so much that there’s a state-run media as you feel like we’re getting close to a media-run state,” says Oliver. “If he’s getting primary information from horseshit commentators on Fox News who directly now have his ear, that’s incredibly dangerous.”

Trump’s second state of the union address, on 5 February, was a case in point. He pushed the faux crisis at the border and said nothing of climate change. Fox’s cheerleaders were thrilled. So were Trump’s Republican enablers, for whom Oliver has open contempt.

“It’s pathetic. It’s utterly, utterly shameful. Unfortunately, it seems to be happening with people who lack the capacity for shame. It is somewhere between disheartening and disgusting to see the extent to which they’ve made a calculated decision that: ‘We can get two-plus supreme court picks out of this, so it’s worth it.’ I would argue it’s not worth it. But they clearly feel differently about it.”

‘I love the idea of being on the receiving end of one of Jürgen Klopp’s hugs, but I’m probably too repressed to enjoy it’ ... John Oliver. Photograph: Alex Livesey/Getty Images

Although he was born in Birmingham, grew up in Bedford and studied at Cambridge, Oliver moved to the US in 2006, married an American (a former combat medic) and instinctively says “we” rather than “you” to his viewers. But he admits the prospect of his two young sons speaking with American accents is strange.

“It never really occurred to me that, if I ever had a child, that child would not sound like me or grow up with some common cultural touchstones,” he says. “I wanted to see what would happen, so I gave [my elder son] some Marmite on toast and he recoiled and I can’t really defend it, I happen to love it. Clearly, it’s not really about flavour; it’s about memories.”

Nor did it occur to him that his children would be denied freedom of movement within the EU. “Brexit happened when he was a few months old. So that was the sad thing, looking at a baby and thinking: your horizons have slightly contracted and you don’t even know it yet. That’s beyond worrying about basically anyone under 25 in the UK and how this is going to fundamentally affect the rest of their life. It’s so sad.”

Liberals emotionally invested in the US and Britain debate which of 2016’s twin catastrophes will be longer-lasting. Oliver is in no doubt: “Brexit is a different level. You do constitutionally know how this [Trump] is going to end: it will either be in two years or six years. Now, the ramifications of what happens in that time, that’s up for debate. But there is a constitutionally mandated end to this.

“Also, at some point, the fact he’s 72 will kick in. He can’t beat death, even though I wouldn’t be surprised if he outlived everybody out of pure spite. But Brexit – who knows where that ends? Maybe it’s a great idea. There’s absolutely nothing to suggest that would be the case.”

Oliver once admitted to having an “immigrant’s crush” on this nation of immigrants. He occupies a fruitful insider-outsider space, delving into domestic politics, such as internet privacy and Vice-President Mike Pence’s pet rabbit, but also zooming out for a global perspective. Last Week Tonight’s much-admired 20-minute segments have focused on topics including the Chinese president, Xi Jinping; Facebook’s dangerous role in Myanmar; elections in India, Mexico and Brazil; and, of course, “a few whacks at the Brexit piñata”. This is like water in the desert for those left parched by America’s TV news networks, which were insular before Trump and now pay even less heed to the wider world. Is Oliver consciously plugging a gap?

“No, I don’t think we’re plugging any gap,” he says. “I think the gap still exists, but it is a problem. It’s difficult, because this country is going through a lot right now, so it’s hard to make the case to viewers: ‘Hey, I know you’re thinking about this one thing right now; I need you to think about the Mexican election.’ That’s a tough sell to the viewers and then, just in terms of how you tell that story, it’s complicated, because the Mexican election did not get a lot of coverage here, even on CNN International.”

John Oliver’s segment on the rise of Xi Jinping.

At the end of the previous season, Oliver and his team of writers, researchers and producers deftly put the US in a wider context as he discussed the rise of Jair Bolsonaro in Brazil and authoritarian leaders around the world. “I guess the thing that was fascinating to me, just as a very broad thesis in that story, was: every time we look at these stories and speak to experts on the ground in those countries, what they’ll usually say is: ‘In America, you’re lucky, because the institutions are holding up.’ The truth is, they’re holding up so far, but institutions in themselves don’t hold themselves up. They’re inanimate objects; it’s people that hold them up. So your last best hope is that Americans will continue to fight back if ever they see a major institution under threat,” he says.

“I think it’s always reassuring when you see pushback to aggressive behaviour from the US government, just like it was edifying to see pushback to America’s drone programme or the NSA, but it’s coming so thick and fast in the Trump presidency. I guess my worry is: how sustainable is this? When do people just start getting exhausted of being outraged by objectively outrageous behaviour all the time? When does it just become the background to people’s lives? Because, at that point, you’ve lost something.”

Such is the Trump marathon. We are all in it together, supporters and detractors alike, surviving one mile and one tweet at a time. How does Oliver keep going? The show itself is cathartic, he says. Then there is his beloved Liverpool football club. “As the world slides further and further away, Jürgen Klopp [the manager] is such an icon of positivity. I love the idea of being on the receiving end of one of his hugs, but I’m probably too repressed to enjoy it.”

For a moment, he is every inch the Briton again, contemplating his favourite forward. “I honestly think that Mo Salah might be my lifeline,” he says. “If he goes, I’ll think: ‘OK, burn everything to the ground.’”

Last Week Tonight With John Oliver premieres in the UK on 18 February at 10.10pm on Sky Atlantic and Now TV