The pictures are appalling, the words terrifying. If Thursday’s opening session is anything to go by, the primetime televised hearings into the storming of Capitol Hill on 6 January 2021 will be both revealing and disturbing. But though their focus is on a winter’s day 18 months ago, they are not about America’s past. They are a warning about its future.

Make no mistake, the revelations of what exactly took place when a violent mob broke into the halls of the US Congress, seeking to overturn a democratic election by preventing the formal certification of Joe Biden’s victory, are a valuable, and shocking, addition to the historical record. The House committee that has been investigating the attempted insurrection for the past year – gathering in excess of 140,000 documents and speaking to more than 1,000 witnesses – discovered that Donald Trump’s response, on learning that the rioters were chanting “Hang Mike Pence”, was to say that his vice-president “deserves” it.

Previously unseen footage and fresh testimony buried the suggestion, made by one Republican congressman, that the behaviour of the insurrectionists of 6 January was like a “normal tourist visit” or that it was, as Fox News’s most watched host, Tucker Carlson, was still insisting on Thursday, no more than a “forgettable, minor outbreak of violence”. Instead, one police officer, Caroline Edwards, who suffered a traumatic brain injury as the Capitol was breached, described being stampeded, knocked unconscious, pepper-sprayed and teargassed. There was so much blood on the floor, she slipped over. “It was carnage,” she said. “It was chaos.”

What’s more, those around Trump knew that the animating cause of this violence was a lie. They knew that Biden had won and Trump had lost. Trump’s attorney general, William Barr, testified that he regarded the claim that the 2020 election was stolen as “bullshit”. Trump’s daughter Ivanka agreed. Plenty of those Republicans in Congress who went along with the lie knew it was garbage – and they knew that they were breaking their oath in indulging it. The investigators revealed that “multiple” Republican congressmen had hastily sought presidential pardons from Trump for what they did, namely trying to overturn a legitimate election.

Some Republicans take comfort from the thought that voters have got other things on their minds just now, that as midterm elections approach Americans will be more preoccupied with Biden’s failures to tame inflation than Trump’s incitement of an insurrection. Petrol at $10 a gallon today will matter more than the gasoline the Republican president threw on the fire of his supporters’ rage a year and a half ago.

Dispiritingly, that view might be correct on the politics. Democrats are unlikely to shift their fortunes in the present by laying out a case, even a compelling one, about the past. But that does not make 6 January a lost cause, still less an irrelevant one. Because none of this is about the past. It is about now.

The most obvious proof is Trump himself. He’s had some setbacks in this primary season, where his favoured candidates in internal party contests have not always prevailed, but his dominance of the Republican party endures. Most assume that if Trump wants to be the Republican presidential nominee in 2024, he will be. Of course, he remains utterly unrepentant about the events of 6 January. On the eve of Thursday’s hearing, he posted on his new social media site that that day “represented the greatest movement in the history of our Country to Make America Great Again”.

But even if Trump does not regain, or attempt to regain, the presidency, he is still part of the US’s future. Whatever his next moves personally, Trumpism is now the defining creed of the Republican tribe. Polls find hefty majorities of Republican voters believing the lie, adamant that Trump was the real winner in 2020. Whether the nominee is the former president himself or a more disciplined politician – the likes of Florida governor Ron DeSantis – Trumpism, with its commitment to permanent culture war and its contempt for democratic norms, is now a central feature of the American landscape.

But here’s why these current hearings should be regarded less as a past judgment than a future warning. On 6 January, the determination of the pro-Trump forces to subvert a democratic election was not in doubt. They failed only because enough restraints were in place to thwart them, whether it was state-level election officials determined to count the votes, and count them fairly, or a court system that threw out wholly groundless claims of electoral fraud. But 2024 will not be the same as 2020. Because Republicans have been busy.

Methodically and across the US, Republicans have been working to dismantle the guardrails that keep American democracy on track. In 2021 alone, at least 19 Republican-ruled states passed measures whose official purpose was tackling (nonexistent) voter fraud but whose practical effect will be voter suppression, making it harder for low-income and minority Americans in particular to cast a ballot – and those efforts are continuing.

More alarmingly, several Republican state legislatures have sought to put themselves or their allies in charge of what used to be non-partisan election machinery, installing Republicans – including “stop the steal” Trump loyalists – in the offices where votes get counted and certified. Worse, there are moves to make state legislatures the sole authority over elections, cutting out the courts altogether: so the Republicans who dominate, say, the Wisconsin legislature could decide that they and they alone will allocate the state’s electoral votes, regardless of who Wisconsin’s citizens actually voted for. Rerun 2020 in this new, altered environment and states that held firm in 2020, giving Biden the victory he had legitimately won, could hand power in 2024 to the loser.

The key shift here is in the Republican party itself. On Thursday night, Liz Cheney, vice-chair of the House committee investigating 6 January, did an admirable job, telling her fellow Republicans that when Trump is gone their “dishonour will remain”. But she is an outlier, isolated and ostracised from her party.

Next week sees the 50th anniversary of the Watergate break-in. But if that event were to happen now, it would play out very differently. The rightwing media would not even cover it, just as Fox did not cover Thursday’s hearing. It’s inconceivable that Senate Republicans would turn on a Republican president the way their predecessors turned on Richard Nixon, driving him from office. We can know that, because they did not turn on Trump.

Nearly a decade ago, the scholar David Runciman wrote a book called The Confidence Trap. It argued that the problem with democracy is that each time it survives a crisis, people wrongly assume that it’s indestructible. We’re confident that democracy can survive anything because it survived the last thing. In today’s America, that confidence now looks badly misplaced. The US only narrowly survived Trump on 6 January 2021 – and the defences that kept the peril at bay are steadily getting weaker.

• Jonathan Freedland is a Guardian columnist. To listen to his podcast Politics Weekly America, search “Politics Weekly America” wherever you get your podcasts