Hope is the thing with feathers, according to Emily Dickinson.

It's also the Arkansas hometown of Bill Clinton and, coincidentally, Mike Huckabee, who for a brief moment looked a promising candidate for the Republican nomination, after his surprise win in the 2008 Iowa Republican caucuses, when he beat a chap called Mitt Romney. And that year it was the word emblazoned on Shepard Fairey's celebrated poster for Barack Obama's presidential campaign.

The authors of the video game Warhammer 40,000: Dawn Of War may not be as highly regarded as Emily Dickinson in literary circles, but may nonetheless have been more realistic when they wrote: "Hope is the first step on the road to disappointment." If there was a dominant theme at the Republican National Convention last week, it was disappointment in President Obama.

This was, of course, a presentational tactic; adopting a "more in sorrow than in anger" tone was a way of criticising the president without appearing too aggressive or engaged in "negative campaigning" – the eventual fate of all campaigns, but which most try not to succumb to until the later stages. But the reason it is a fairly sensible presentational tactic is that it is so clearly in tune with the American electorate's feeling about Obama.

That disappointment was perhaps inevitable, given the wave of optimism which prevailed when he won, and the horrendous state of the world economy since. Indeed, at most other times, the American economy alone would be enough to do for his chances of re-election, even though sitting presidents are generally reckoned to have a strong advantage.

What's more, by any objective judgment, President Obama's plumage has moulted. In part, that is because the economy has given him a tough hand to play, but it is also a reaction to the over-enthusiasm which greeted his election. Like so many political leaders, he disappointed his natural supporters by failing to deliver on much of what they expected. Simultaneously, he managed to confirm all the suspicions of the many Americans who regard him as a dangerous leftie.

With the exception of healthcare – and even there his plans were watered down and the material changes are more of a handout to the private health insurance industry than a benefit to pensioners and the poor – it is hard to think of any major achievement.

The hopes of civil libertarians encouraged by his pronouncements on Guantanamo have not merely been unfulfilled but also dashed: the president now has weekly meetings to authorise the extra-judicial killings of suspected terrorists by remote-controlled drones, while Bradley Manning has been detained for more than two years without trial for his alleged part in leaking government information.

The national debt is more than $16 trillion and rising by nearly $4 billion every day. Unemployment is above 8% for the 43rd month in a row, and growth is sluggish at around 1.5%.

Though it would be hard to tell from British television coverage, where almost all the reporters are much better disposed towards the president than most Americans – something, in fairness, that they share with most people on this side of the Atlantic – disillusionment is widespread not only among the usual suspects, like the Tea Party tendency, but many of President Obama's former supporters.

All this ought to present an open goal for the president's opponents. Yet until last week, it was hard to discern any notable enthusiasm for Mitt Romney – not that there was any sign of much more for any of the other potential Republican candidates for nomination.

To be sure, Romney is not a naturally inspiring or charismatic politician, but he also has the electoral disadvantage of being seen as a political insider (his father was Governor of Michigan). His being a millionaire is no disadvantage – besides, it is more or less essential for any candidate – but the fact he made his money in a private equity firm isn't much of a vote winner these days. What's more, Mr Romney's record as Governor of Massachusetts, though fiscally successful, was considerably more socially liberal than the mainstream of Republican support and, for that matter, most non-metropolitan Americans. Among his measures, he introduced healthcare reforms remarkably similar to the Obamacare he is denouncing.

Some commentators believe Mr Romney's shift to the right is a matter of simple electoral mathematics; in order to win, the Republicans, whose natural demographic support is a minority, need to galvanise as many natural libertarians and Bible Belt conservatives as possible – the sort of voters who loved Sarah Palin, and the sort of Americans whom most Europeans seem not to understand at all.

This accounts for the selection of Paul Ryan, just that kind of conservative, as Romney's running mate – though Mr Ryan is altogether more credible and competent than Palin. Despite the surreal spectacle of Clint Eastwood, Mr Ryan's speech was undoubtedly the highlight of last week's convention in Tampa.

It is true that, shockingly for a political speech, the vice-presidential candidate advocated inconsistent policies, played down the Republican programme's similarities to the president's, and was misleading, if not technically dishonest, about the closure of a car plant in Wisconsin which Barack Obama had said he hoped to save. But none of that mattered beside the overall tone.

The areas Mr Ryan emphasised were the quintessential qualities of small-town America, and those which people who have little experience of the majority of the US have the most difficulty understanding. They are self-reliance, fiscal and social conservatism, aspiration, a distrust of the state, and a preference for decision-making at community rather than national level. Far from being the concerns of a few Tea Party nutters and Idaho survivalists, as many imagine, these concerns are central to many US voters.

Rightly or not, they see their current president as the antithesis of this spirit. If Mr Ryan can perform the unlikely trick of persuading them that Mitt Romney embodies these qualities, the election may be much more interesting than seemed possible just a couple of months ago. The Republicans now have a hope.