He was described as the most important politician of 2020. James Clyburn’s endorsement performed a political defibrillation on Joe Biden’s flatlining campaign, reversing his fortunes and sending him on his way to the White House.

Midway through Biden’s first term, the South Carolina congressman has no regrets. On the contrary, as America’s first octogenarian president spends the holidays deciding whether to run for re-election in 2024, Clyburn is backing him all the way.

“I’m supporting him and I hope he makes that decision too,” he tells the Guardian by phone. “He’s delivered for this country. He’s put this country back on track towards a more perfect union. If you look at the production of his administration in this Congress he’s had to work with, we’ve been the most productive since 1965.”

Biden’s roll call of legislative achievements includes coronavirus relief, infrastructure investment, historic climate spending, a boost for computer chip manufacturing and scientific research and measures on gun safety and military veterans’ benefits. And like a unicycle juggler on a tightrope, he did it with tenuous majorities in the House and Senate.

Clyburn adds: “Joe Biden has delivered exactly what the country needs and that’s why we were rewarded the way we were on [midterm] election day. There were people predicting there was going be this ‘red wave’ and Democrats were going to lose by 60.”

They lost only by nine, largely due to redistricting in California, Florida and New York.

But doubts remain. While Biden often maintains a punishing schedule and grills his aides on minute policy details, there are moments when the 80-year-old mangles words and looks his age. Polls suggest many voters feel he is too old for the job. He is older than Ronald Reagan was when he completed his second term. If Biden serves a full second term, he will be 86 at the end.

Clyburn is something of an expert on this issue: he is 82 and not slowing down. He speaks to the Guardian having attended a state dinner with the French president Emmanuel Macron that went well past midnight, then appeared on MSNBC at 8am. A couple of days later he will have a late night at the John F Kennedy Center for the performing arts honours ceremony. He also finds time to pump out a podcast, Clyburn Chronicles.

Clyburn will remain in leadership when Democrats become the minority in the House next month. While the outgoing speaker, Nancy Pelosi, 82, and 83-year-old majority leader, Steny Hoyer, are making way for a new generation, Clyburn will serve as assistant Democratic leader, the number four position.

He explains: “If we are going to regain the majority, we’re going to have to do so maintaining some stability in our caucus, being inclusive in our caucus and, if you look at the leadership table, the south is not represented there. Rural America is not represented there. I represent both.

“The majority of Black people in this country still live in the south and for some strange reason every time people start talking about African Americans, they start talking about inner-city New York, Philadelphia, Chicago. That’s not where African Americans live. That’s where the media focus and one of the reasons our party is not doing as well as we should is because we have not developed the kind of rural policies that we need to develop.

“That’s why I was so much of a stickler for broadband being in the infrastructure law. That’s why I’m always pushing for community health centres, because I can assure you where we have this kind of attention being paid to people’s healthcare needs, to their housing needs, is where we do better.”

The new House Democratic leader will be Hakeem Jeffries of New York, the first Black person to head a party in Congress.

Clyburn reflects: “The first, always you’ve got to be happy, but you want to make sure that the first performs in such a way there won’t be a problem getting the second.

“When I was first elected to Congress, I was 52 years old. That’s the age Jeffries is today and getting elected leader of our caucus. That’s the way things work. My dad was not allowed to get a college degree because of state law and so I came here to Congress at 52. He’s the leader of our caucus at 52. That’s how things evolve.”

Republicans will have the speaker’s gavel. Kevin McCarthy’s struggle to win election is indicative of a potentially bumpy ride as moderates clash with far-right members. Marjorie Taylor Greene of Georgia, once seen as fringe figure, is backing McCarthy and might soon be calling the shots. Some observers fear the party will give fresh impetus to white nationalism and political violence.

Clyburn says: “I have no fears of that. These people are going to do what they want to do and I would hope that the Republicans would put the needs of the country above the partisanship of any one person in their party. If they go down that road, they are going to have to deal with failure. It’s just that simple.”

Donald Trump’s influence over Republicans appears to be diminishing in the wake of the midterms, a series of self-inflicted wounds and a damning report by the House January 6 committee. But Clyburn, who has compared Trump to Benito Mussolini, is not writing him off yet.

“Trumpism is still there. It’s still a big deal. Trump brought a lot of people out from under the rocks that they’d been hiding under and so long as he’s out there, these people are going to be out there. What we’ve got to do is be very careful. Thomas Jefferson is sometimes credited with having said: ‘ternal vigilance is the price of liberty.’”

So what does he make of Trump’s most likely rival for the 2024 Republican nomination, Ron DeSantis of Florida?

“He’s more moderate and just as dangerous because the policies are the same. Trumpism is Trumpism, no matter where it comes from. These -isms, you have to be careful with.”

Some Democrats might be tempted to say better the devil you know. Trump has lost election after election. If he is the Republican standard bearer in 2024, polls suggest he will lose to Biden again. But Clyburn is not rooting for Trump to be the nominee.

“We need to have a legitimate, serious discourse when we decide on the presidency,” he says. “I don’t want to win the presidency by default. I want to win the presidency by having the best proposals.”