It’s been 28 years since adviser James Carville helped propel Bill Clinton to the presidency by posting a sign in campaign headquarters reminding everyone there: “It’s the economy, stupid.” That was his singular way of drilling home the message that the economy mattered more to voters than anything else.

So far in 2020, though, it doesn’t seem to be the economy. Even though voters today prefer President Trump to handle the economy as much as ever, he remains behind as the race enters its final two weeks. That raises two questions: Why? And could the economic issue still propel him to a final-days turnaround?

Five times this year, The Wall Street Journal/NBC News poll has asked voters who they think would be better at handling the economy, Mr. Trump or Democrat Joe Biden. Five times they have named the president, by margins ranging from seven to 11 percentage points. Plenty of Americans, in short, appear to buy the president’s argument that the economy was in fine shape before the coronavirus hit, and that it isn’t his fault it has plunged since then.

More than that, when the poll asked voters just last week which issue is most important to them, they named the economy more than any other issue, including the coronavirus. All of that simply serves to frame the mystery of why that set of conditions isn’t working better for Mr. Trump.

The answer starts with evidence suggesting the dominance of the economic issue may be something of a myth, which has its roots in that 1992 campaign. It simply isn’t true that the candidate or party given better marks on handling the economy wins an election, even when the economy seems to get top billing. Voters have other issues propelling them with nearly equal force—and sometimes they view those as matters that also affect their own everyday economy.

Bill McInturff, a Republican pollster who co-directs the Journal/NBC News poll, notes that the same set of conditions prevailed in 2018: Voters said they thought Republicans would do a better job handling the economy, yet the party lost 41 seats in House elections that year. In some respects—the shift of suburban women toward the Democrats, more energized minority voters, concern about health care—this year resembles 2018 more than 2016 when Mr. Trump won.

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And though it’s little remembered now, a similar set of circumstances prevailed in 2012. Voters called the economy the most important issue, and more said they preferred Republican Mitt Romney to Democratic President Barack Obama on handling it. Yet Mr. Obama won re-election.

Then, as now, there was a cluster of other issues that, when taken together, rivaled the economy in importance to voters. This year the coronavirus, health care, race relations, climate change and ability to unite the country also are pressing and emotional matters for many voters. On every one, voters tend to prefer Mr. Biden, sometimes by wide margins.

More broadly, now as in 2016, the race seems as much about a struggle over the nation’s culture as about economic issues.

Moreover, voters relate the health of the economy to the handling of the pandemic: If they buy Mr. Biden’s argument that the economy can’t improve until the coronavirus is under better control, they actually see the pandemic as an economic issue. That benefits Mr. Biden.

Democratic pollster Peter Hart, who helps oversee the Journal/NBC News poll, says that as Americans already are standing in long lines to cast ballots, 2020 is a year in which voters see the broader course of the country as the real issue. “The massive turnout in 2020 is occurring because voters understand the stakes that go far, far beyond the two candidates,” he says. “Hidden behind the pandemic are the big issues of race, climate, gender, and safety.”

Mr. Trump also hasn’t played his advantage on the economy particularly well. He talks about his record of accomplishment, but doesn’t lay out many specifics about what he’d do in a second term to revive and extend economic growth. And his fabled rallies tend to veer down side alleys as they did in Michigan on Sunday, when the president’s argument that Michigan Democratic Gov. Gretchen Whitmer needs to do more to open up the state’s economy veered into chants from the crowd of, “Lock her up.” Mr. Trump echoed “Lock them all up” just days after the FBI arrested a group of men for plotting to kidnap the governor. That put the emphasis on a divisive message rather than a unifying economic one.

Perhaps Mr. Trump will find better ways in the campaign’s final days to focus voters on the economy, to his benefit. Presidential elections tend to tighten in the end, as wandering voters return to their home base, and as candidates manage to frame the final choice to their benefit. Mr. Trump gets one more big chance, in Thursday’s debate, to bring the argument back to the economy.

Write to Gerald F. Seib at jerry.seib@wsj.com