The vast collections of the Smithsonian Institution in Washington contain two brown wooden chairs. Their backs have labels explaining that they were used by John F Kennedy and Richard Nixon in “the first face-to-face discussion between presidential candidates” at the CBS television studio in Chicago in 1960.

In short, the first televised presidential debate. And where America led, the rest of the world followed, copying the model of gladiatorial political combat as the ultimate format to help voters make up their minds.

But heading into the US midterm elections, the debate appears to be in decline, a casualty of fragmented digital media, a deeply polarised political culture and a democracy losing its sense of cohesion.

For many Republicans, ducking debates is a way to express disdain for a national media that former president Donald Trump has derided as “fake news” and “the enemy of the people”. Some Democrats have a different motive, refusing to share a platform with Republican election deniers peddling baseless conspiracy theories.

In Arizona, for example, Democratic gubernatorial hopeful Katie Hobbs has declined a debate with Republican Kari Lake, a telegenic Trump supporter who has pushed his “big lie” that the 2020 presidential election was stolen.

But Republicans are the main objectors. In Nebraska, gubernatorial candidate Jim Pillen has refused to debate Democrat Carol Blood. Pillen’s campaign manager, Kenny Zoeller, told the Nebraska Examiner that “he doesn’t do political theater”.

In the Pennsylvania’s governor’s race, Republican extremist Doug Mastriano has rejected a televised debate with an independent moderator. Instead he has reserved a hotel ballroom on 22 October and selected a partisan to referee: Mercedes Schlapp, who was strategic communications director in the Trump White House. Democratic rival Josh Shapiro has little incentive to accept.

In North Carolina, Ted Budd, who sat out four Republican primary debates in his Senate race, has said he will not accept an invitation from the North Carolina Association of Broadcasters to debate Democrat Cheri Beasley. Budd said he had accepted a cable debate invitation, but there is no agreement with Beasley about that appearance.

It is a sorry state of affairs for a time-honored tradition that America exported around the world. Even Britain, after decades of resistance, followed suit in 2010 with three leaders’ debates between prime minister Gordon Brown, Conservative David Cameron and Liberal Democrat Nick Clegg.

“Believe it or not, I watched all four of the Kennedy-Nixon debates and you could hear a pin drop anywhere you went,” said Larry Sabato, director of the Center for Politics at the University of Virginia. “Everybody was watching. In fact, over 70m watched and the number of votes that year? 70m.

“But in the era of 400 channels, when polarization is so intense that the vast majority of voters already know for whom they’re voting, it doesn’t matter what happens in a debate or if there is a debate. The costs of not debating are very small. ”

The format is not quite dead yet.

In Pennsylvania, Democratic Senate candidate John Fetterman has agreed to one contest with Republican nominee Mehmet Oz, while in Georgia, Democrat incumbent Raphael Warnock and Republican challenger Herschel Walker (who dodged primary debates) appear to be inching closer to a deal.

In Michigan, after prolonged wrangling, Democratic governor Gretchen Whitmer and Republican nominee Tudor Dixon finally agreed to a single debate next month.

Florida Republican Governor Ron DeSantis is set to debate Democratic challenger Charlie Crist but only once and only on a West Palm Beach TV station. In Texas, Republican governor Greg Abbott has granted a single debate to Democratic challenger Beto O’Rourke – but it will be on a Friday night and competing for eyeballs with the high school American football season.

In each case, the enthusiasm to debate is underwhelming: candidates appear to be looking for an excuse not to do it in a divided America where the sliver of undecided voters offers diminishing returns.

They turn instead towards partisan echo chambers aimed at motivating turnout from their own bases. Republicans, in the particular, have been snubbing the mainstream media in favour of fringe rightwing outlets during the campaign so far. It is one more blow to the idea of communal experience, shared reality and the glue that holds democracy together.

Elaine Kamarck, a senior fellow in governance studies at the Brookings Institution in Washington, said: “It’s dangerous because these televised debates at all levels have been one of the few good things about democracy in the modern era. People had to stand up there and defend themselves and say what they believed and let the voters take a good look at them.”

But Kamarck, who worked in the Clinton White House, remains optimistic that the shift is not permanent. “It is driven by a group of Republican candidates who are very inexperienced and ideological and know that they can’t do well in a debate because there’s so many things that they are for that are either unpopular or indefensible in terms of policy.

“What you see here is a Republican party that’s gone off the rails led by Donald Trump. It is this year’s crop of candidates who are not very serious people and can’t debate but I do think debates will return when the Republican party starts nominating normally qualified people to run.”

The acid test will come in 2024. From Ronald Reagan’s “There you go again” tease of Jimmy Carter, to George H W Bush’s ill-judged glance at his watch, to Trump’s apparent threat to jail Hillary Clinton, presidential debates have provided marquee moments even though, in truth, they may not have changed many minds.

There was an ominous sign earlier this year when the Republican National Committee, which has proved a cheerleader for Trump, voted unanimously to withdraw from the Commission on Presidential Debates, which was founded in 1987 to codify debates as a permanent part of presidential elections.

Aaron Kall, director of debate at the University of Michigan, who attended presidential debates over the past two cycles, said: “One of the great things about a debate is seeing a candidate have to deal with a question maybe that they didn’t think of or they didn’t plan for and, under pressure, how they address that.

“When we’re looking for candidates for these really important positions we want to see – how they answer the 3am phone call or deal with something unexpected. It’s pretty good on the job training and rehearsal for the actual job over an hour and a half. We have all these different ways in which to evaluate the strengths and weaknesses of candidates and it’s just another one that is going by the wayside.”