Kamala Harris has made a dream start. But it's too early to count out Donald Trump | Jonathan Freedland

Everything is going right for her and wrong for him. Kamala Harris has the encouraging poll numbers and, more precious still, the momentum. Donald Trump has the serial errors, the maudlin introspection and wobbling campaign team. In less than three weeks, the Democrats have pulled off one of the most extraordinary turnarounds in US political history, replacing a candidate who was shuffling towards near-certain defeat with one apparently soaring towards possible victory. And yet, even as Harris speaks of bringing the joy, contained within is a lurking danger - a peril that should be all too familiar.

The sources of joy are not mysterious. Democrats are heading to Chicago for a convention that will feel like a party but was set to be a wake. Before 21 July, they were tied to Joe Biden, a man whose presidency has proved far more consequential than most predicted but who was on course to lose and lose badly in November. His passing of the baton to his number two has gone better than anyone had any right to expect.

All but seamlessly, the campaign has switched over - equivalent to rebuilding a plane in mid-air, say seasoned election hands - and the candidate herself has taken to the task with unexpected ease. Twenty years younger and a whole lot more vigorous than her opponent, she has turned what had been Trump's most potent weapon against Biden - age - against Trump himself. He is now the candidate of the past, she the face of the future. Never mind that Harris is a senior member of the present administration, she has shaken off the burden of incumbency - currently a negative in most democracies across the world - and cast herself as the turn-the-page option, aided by a powerful slogan: "We're not going back."

The evidence that it's working is in the headline poll numbers, which show her edging ahead in the very battleground states where Biden had been trailing. Almost overnight, she is winning back the voters who propelled Biden to victory in 2020 but were drifting away from him in 2024: young, Black and Hispanic Americans. Drawing big crowds, inspiring a thousand social-media memes, she is generating something Democrats have not seen since the first Barack Obama campaign of 2008: excitement.

All this is having an equal and opposite effect on Trump. The better her numbers or crowds get, the more gloomy and rattled he becomes, consoling himself with the delusion that photos of Harris's massive audiences are AI fakes. The New Yorker's Susan Glasser depicts Trump as bereft, missing Biden as he pines for the return of the man he knew how to run against. That contest was simple: it was strong v weak, with Biden's age doing the work.

But now Trump faces Harris, and he can't quite work out how to take her on. He can't fix on a nickname, he can't settle on a target. His team wants him to run on immigration and inflation - both Democratic vulnerabilities - but he keeps returning to the terrain he knows best: culture wars and race baiting. Just as he once falsely claimed that Obama was not born in the US, Trump initially offered his theory that only late in life did Harris happen "to turn Black". He also regularly describes the vice-president as a "low IQ individual", a phrase he has long applied to Black female politicians. His base may like this talk, but it repels everyone else.

An illustration of the unsettling effect Harris is having on Trump came in the mutual back-scratch he conducted with X magnate Elon Musk this week. "She looks like the most beautiful actress ever to live," Trump said about a drawing of Harris on the cover of Time magazine. "She looked very much like our great first lady, Melania," he added, referring to his wife. Along with any listener to that exchange, Trump doesn't know where to put himself.

Because he is knocked off balance, he keeps stumbling. The Musk encounter was a case in point. After the embarrassment of a tech breakdown that led to a start delayed by 40-plus minutes, Trump rambled for two hours, straying into baffling tangents and frankly weird claims. One example: "global warming" is no threat, because rising sea levels mean "more oceanfront property". (The real danger, he said, is the warmth of nuclear weapons.) What's more, Trump seemed to speak with a heavy lisp throughout. None of this might matter much in itself, but it shows that Trump is beginning to get some of the same scrutiny of his cognitive and physical capacities that drove Biden to step aside. Put simply, age is now his problem.

So this race is going exactly the way Harris would want it to go. Trump is lashing out at allies and, always a sign of a troubled campaign, shaking up his team. He is saddled with a running mate whose back catalogue would make a Gilead commander blush, while he paints an ever-darkening picture of a US in decline, a nation riddled with crime and overrun by scary invaders. All the while, she is beaming about a brighter tomorrow. As the Republican sage Mike Murphy puts it, "He's doing Voldemort and she's doing Ted Lasso."

Where, then, is the danger? First, the polling is not quite as rosy as Democrats want it to be. Dig further into the numbers and you see that, despite everything, Donald Trump is more popular now than he was at this same, mid-August point in either 2020 or 2016. His approval rating currently stands at 44%. In August 2016, a paltry 33% of Americans had a positive view of him - but he went on to win.

What's more, in each of the three crucial battleground states of Pennsylvania, Wisconsin and Michigan, Harris is ahead by only four points, according to the latest survey. That's welcome progress, to be sure, but it's not enough when you recall that Trump put on nine points between August and November in those states in 2016 and closed the gap to a photo-finish in 2020.

Harris may be more charismatic than either of the Democratic standard-bearers in those earlier contests, but she has vulnerabilities of her own. She is clearly a figure of the "coastal elites": a wealthy Californian, she has no equivalent of the Scranton Joe persona available to Biden. Both she and her running mate, the Minnesota governor Tim Walz, have a history of progressive positions that anyone with a memory knows Republicans can twist into a caricature of leftwing radicalism. True, Walz's vibe is cuddly midwestern dad - and there's good evidence that, these days, a politician's vibe matters more than their record - but there's still a job to do. It's almost a universal truth of contemporary politics that any party not of the right has to go much further than it would like to reassure voters in the centre. (Just ask Keir Starmer.) By that measure, the Democratic nominee may still have some distance to travel.

Above all, and paradoxically, it's Harris's astonishing early success that contains risk. It has encouraged Democrats to believe that, in ditching Biden, the hard work has already been done, that the menace of a second Trump presidency has been averted. But this remains a perilously close contest in a sharply divided nation. As we have seen twice in recent years, Republicans enjoy a structural advantage in the electoral college that means that a Democrat can win the popular vote by a resounding margin - and still lose.

So, yes, Harris has made a dream start. Trump is flailing. But it is far, far too early to celebrate. In the autumn, Americans will take their traditional second look at the two candidates. There will be TV debates and the hard yards of getting voters not to share memes on TikTok but off the couch and to the polling booth. This race is far from over - and if the last, turbulent decade has taught us anything, it's that it is always too soon to count out Donald Trump.