As President Donald Trump has been forced to swat away persistent questions buzzing in his ear about signs of a recession on the horizon, the clock continues to tick toward the 2020 election and the economy becomes increasingly framed as a campaign issue.
For decades, political scientists (and campaign advisers) have tried to get to the bottom of why voters check the boxes they do. For presidents, the economy has historically been one of the key drivers of election wins, traditionally only falling behind war time issues in importance.
What’s less clear is how voters judge the economy’s health and how much policy initiatives and campaign promises, like tax cuts, can tip the scales. In general, decades of studies and research have shown voters to be sociotropic, considering wider economic conditions over their own personal (pocketbook) finances. Still, many of the nuances of voter behavior around the economy are the subject of vigorous debate.
For starters, voters tend to have what experts call “myopia,” or a shortsighted view. An incumbent’s share of the popular vote is largely correlated to GDP growth in the year of the election, but adding economic data from previous years does not improve election projections, according to Vanessa Williamson, public policy researcher and author of Read My Lips: Why Americans Are Proud to Pay Taxes.
While the models predict the popular vote well, she added, that does not always equate to a victory in our electoral college system.
The idea of what weighs more in the voters minds—their family’s personal finances or the general welfare of their community and the nation—is an ongoing heated debate among experts.
“On balance people weigh the whole economy more heavily than personal or family income,” University of Iowa political scientist Michael Lewis-Beck said, adding that surveys show that voters impressions of the economy correlate strongly to GDP growth in any given year.
“The pocketbook is weaker than the sociotropic influence but it’s not zero,” he said. “If they are suffering, they may not be likely to vote at all, or if they do, they are more likely to vote against the incumbent. It’s not as big an effect as if they judge the whole economy as suffering.”
While the economy is often a key variable in an election outcome, some research has shown that despite positive economic factors in an election year, media coverage can influence the perception of the economy enough to shift votes.
In a study of Bill Clinton’s win over George H.W. Bush in 1992, political scientist Marc Hetherington found although the early ’90s recession had technically ended by election year and GDP was once again positive, persistent coverage signaling an ongoing fiscal crisis negatively colored voters perceptions, swaying them to the Democrat.
Additionally, recent studies indicate the voter’s “patrimony,” their land, property, and assets outside of a typical salary, also plays into their choice, as those with more resources tend to vote Republican. That may be a concern for the GOP, as the U.S. homeownership rate fell in the first quarter for the first time in two years and is at a 50-year low for African Americans.
The economy has grown under Trump, and by some indicators—unemployment rate, consumer confidence, productivity—is healthy. Other signs are less promising. A recent trend of rising wages appears to be stalling as blue-collar job growth is at its lowest level since Trump’s inauguration. Surveys show manufacturing activity is falling toward recession levels.
“Unemployment rates may be low, but that doesn’t account for people who have stopped looking for work,” Lewis-Beck said. “And if people are working two to three jobs to get by, sure they have a job, but they are scrambling to pay rent with multiple jobs. That’s not a good economy.”
Taking a look around the globe, several nations are teetering on the brink of extended contraction. Three of Europe’s four largest economies, the United Kingdom, Germany, and Italy, are on the path to recession by the new year. China is growing at its slowest pace in 27 years, and Japan appears headed for recession, as well.
Trump’s signature domestic economic initiative, the Tax Cuts and Jobs Act, also may have come too early in his presidency to give him any noticeable election-year boost.
“Voters have previously forgotten much larger and more popular middle-class tax cuts,” said Williamson, also a senior fellow of governance studies at the Brookings Institute, arguing early cuts under George W. Bush and Barack Obama did little to boost their polling later in their terms. “In general American’s don’t recognize the benefits of public policy done through the tax code as well as they do more direct and straightforward programs such as Social Security.”
Polling indicates presidential approval rates are growing less closely related to the state of the economy, according to Williamson, a trend she first noticed under Obama but has grown stronger with Trump’s first term. The most recent Gallup Poll had both “government/poor leadership” and “immigration” ahead of economic issues as the nation’s “most important problem,” and the percentage of people placing economic problems at the top of the list is steadily falling.
“We are living in a time of extremely high partisanship and that does explain a lot,” she said. “Partisanship is swamping other considerations and makes it less likely to see changes in attitude.”
Nonetheless, the economy is still the crux around which successful campaigns are built. In her book, The Message Matters, UCLA public policy professor Lynn Vavreck argues campaign fortunes are intricately linked to the economy and messaging.
In boom times the challenger must run an “insurgent campaign,” hitting on a new, salient issue where the incumbent has a less popular position. In contrast, the incumbent runs a “clarifying campaign,” consistently highlighting the economy. John Kennedy and Jimmy Carter were “insurgent candidates” who defeated incumbents backed by strong economies because they hit on issues of U.S. military inferiority to the Soviet Union and Washington, D.C., cronyism and corruption, respectively.
While voters still play close attention to the economy, how they score may be changing.
“One thing I’m seeing that is more in play than before is inequality,” Lewis-Beck said. “Historically people in the U.S. don’t care much about inequality, they cared more about opportunity to get ahead and climb to the top … That’s starting to change and is coming to the fore as inequality gets more severe, and it hasn’t been used much as an issue in past elections.”
More must-read stories from Fortune:
—Will gaffes hurt Biden’s chances of a 2020 win? Strategists are divided
—These are the 2020 senate races to watch
—What is BDS? Boycott, Divestment, and Sanctions explained
—When does Congress reconvene? August recess, explained
—Trump thinks he is winning the trade war, but the data tell a different story
Get up to speed on your morning commute with Fortune’s CEO Daily newsletter.