Even the finest political insights congeal into received wisdom over time. Then they rot into banality. When James Carville, Bill Clinton’s campaign strategist, first pinned a reminder in his office to focus on, among other things, “the economy, stupid,” he could not have known that this morsel would still be reheated and served up on Westminster menus 22 years later.

Carville’s aide-memoire gets an outing whenever politicians are losing an argument about something that isn’t the economy and want to pretend it doesn’t matter. It’s the first commandment: thou shalt have no other issues before me.

It’s what senior Labour people were saying at the start of their conference, when the Tories were broadsiding them with demands for English votes for English laws in parliament. Let Cameron waste his ammunition on the West Lothian question, Ed Miliband’s aides said. The voters want to hear us talk about the scourge of low pay.

Carville’s dictum also comes out when the Tories face Labour accusations that they can’t be trusted with the NHS. The riposte is that the health service needs money that can only be generated in a growing economy, for which only Conservatives have a credible plan. So really, it’s the economy, stupid.

Obviously voters will tend to prefer a party that secures their financial interests. Or, more precisely, they will avoid one if they think it might ruin them. But that doesn’t help a leader build a winning campaign if no one can agree on which part of the economy it really is, stupid.

For the Tories, budget discipline is paramount. They have successfully written their version of events into the national economic story, with the first test of a sound government set as its stomach for austerity. This isn’t quite the same as success in reducing the deficit or national debt, on which measures George Osborne’s record is flimsy. Government borrowing in September was £1.6bn higher than the previous year. The chancellor gets away with it because so few people think Ed Balls would have done a better job.

Miliband’s hopes instead rest on polling in which voters say they are unimpressed by a recovery that isn’t showing up in their payslips. The Treasury insists this is a standard feature of the post-recession landscape and that wages will pick up. Miliband says it is a deep structural flaw in the economy that, if unaddressed, will blight the prospects of British workers for a generation. “We’ll hammer the Tories on wages,” a Labour strategist told me earlier this year, although so far the attack has had all the impact of an occasional prodding with a foam mallet.

Downing Street takes comfort from opinion polls that put Cameron and Osborne well ahead of Miliband and Balls on who is better trusted to run the economy, but, given the double-digit scale of that advantage, the question really ought to be why the Tories aren’t also miles ahead in party preference. One explanation, put forward by Tory liberals, is that Cameron has been dragged off course by his party’s rebellious Eurosceptic fringe and sucked into an unwinnable anti-immigration arms race with Ukip, when he needs to get back to the economy. Conservative strategists say he will do just that when the time is right. Treasury attack dossiers are being compiled to show that Labour numbers don’t add up. Accommodating business leaders will be lined up to warn of the perils of wealth-crushing “Red Ed” leftism.

The one explanation for polling stagnation you never hear from Tories is that Miliband’s account of a recovery that bypasses the majority may just be right. The ineffectiveness of Labour’s campaign doesn’t disprove the analysis that underpins it.

There are many reasons for the growth of Ukip support, but surely a big one is resentment at the unfair allocations of reward in the boom years, and pain after the bust. You don’t have to be a card-carrying Marxist to see that a crisis of confidence in the political establishment may have its roots in economic dysfunction. Cameron himself came close in 2009, when he went to the World Economic Forum in Davos and warned of “markets without morality”, “wealth without fairness”, “a disconnection between capitalism and people’s lives”.

But that was a different Cameron incarnation. This was around the time that he was talking about the “big society” as a civic, voluntary alternative to state intervention. The idea flopped and the phrase is now banished from the Tory lexicon. It wouldn’t in any case look very appetising suddenly regurgitating five years later, but the insight that lay behind it was sound. Elections are never won by a kind of crass Carvillism – the view that voter behaviour tracks national economic indicators – and certainly not by Conservatives who must always battle the perception that they accept social decay as a price worth paying to balance the books.

Notably, in 2012 Carville himself revisited the old slogan in a book – It’s the Middle Class, Stupid – arguing that the new electoral battleground was insecurity and income stagnation, which rob mainstream America of attainable dreams of a more prosperous future. The book was co-authored with Stan Greenberg, Clinton’s pollster, who has also advised Miliband.

Tory majorities from Macmillan to Major have been won when enough voters feel the party offers them ladders to climb, removing obstacles to their advancement into an expanding middle class. Cameron sometimes talks in those terms. He fiddles around the margins of unequal opportunity – offering soft loans for first-time property-buyers, for example. But his favours have been more conspicuously bestowed on people for whom the great recession was an minor inconvenience, or no inconvenience at all.

The Tory quandary is all the more severe now that British politics has fragmented into a multiparty melee. Labour’s share of the vote is shrinking, but Cameron is not yet the beneficiary. He may be cooking up a campaign to crush Miliband, but his isn’t the only restaurant in town and it has been serving up the same economic argument for nearly five years. If voters are turning up their noses, it could be because they aren’t stupid.