In a paper published last month, Princeton economists Anne Case and Angus Deaton showed that over the last 15 years, white middle-aged Americans have been dying at unusually high rates. Most of those deaths were concentrated among people with only a high-school diploma, or less.

Polls say that the same kind of people — older, less-educated whites — are largely responsible for Donald Trump's lead in the race for the Republican nomination for president.

This could be a coincidence. But it is nonetheless striking that Trump’s promise to "Make America Great Again" has been most enthusiastically embraced by those who have seen their own life's prospects diminish the most — not in terms of material wealth, but in terms of literal chance of survival.

Case and Deaton’s work has attracted some controversy. There's debate over whether the death rate has actually risen for white Americans aged 45-54, as they claim, or if it has just remained the same over the past two decades. But even their critics concede that the bigger picture is alarming.

In countries such as Canada, the United Kingdom, France, and Germany, middle-aged people has been dying at ever-decreasing rates over the last 20 years. Middle-aged African-Americans and Hispanics in the U.S. have experienced similar trends: declines in the mortality rate of about 27 and 19 percent, respectively, since 1999.

But something is wrong with white America — particularly, less-educated white America. Between 1999 and 2013, the death rate for middle-aged white people, age 45 to 54, increased by 9 percent, according to the paper. For middle-aged white people with a high school education or less, the death rate went up 22 percent.

Now compare that to data from a new Washington Post-ABC poll, released Tuesday, which shows that Trump supporters are disproportionately white Americans without college diplomas. Among Republican-leaning registered voters, 46 percent of them support Trump, compared to 38 percent of Republican-leaning registered voters overall who support Trump.

Case and Deaton blame dramatic spikes in poisonings (including drug overdoses), suicides, and liver disease as the main causes for the rising death rate among middle-aged white Americans. These problems have been most acute among the less-educated. Among those with no college, poisonings tripled between 1999 and 2013; suicides went up by 78 percent; death by liver disease increased by 46 percent. 

In other words, what's killing middle-aged whites is the opioid epidemic. It's depression. It's alcoholism.

These are, at least in part, diseases of despair and diminished opportunity. And it's not too much of a stretch to connect this suffering to the economic forces that have hollowed out the middle and working class in recent decades and imposed pain on those without higher education.

It has never been more of a disadvantage to lack college credentials. In 1979, people with four-year college degrees earned about 35 percent more than those without, according to research from the Federal Reserve Bank of San Francisco. In 2013, the college wage premium was 80 percent.

This is not to say that the college-educated are much better off today than they were 30 years ago. They're not. The widening gap in wages reflects that life has been getting worse for those with only a high school diploma.

Case and Deaton point out that less-educated citizens of other countries have faced similar economic challenges like wage stagnation and inequality, and yet their death rates have been going down. So the economy does not provide a completely satisfactory explanation for why middle-aged whites in America are doing so poorly.

But what matters in politics is people's perception of the situation. On the stump, Trump likes to blame immigrants for the nation's economic woes. "They’re taking our jobs. They’re taking our manufacturing jobs. They’re taking our money. They’re killing us," he said in July. This message has resonated with voters.

As the latest Washington Post-ABC News numbers show, Trump finds particularly strong support for his immigration stance among Republican-leaning whites without college degrees. About 52 percent of them say they trust him the most to handle immigration issues. They also like his views on terrorism, believe he is the strongest leader, and also the most likely to get elected.

There is real unhappiness among less-education middle-aged whites in America, dissatisfaction and suffering that goes beyond what the bleak data on wages tell us. Case and Deaton's research suggests that many who fit the Trump voter demographic are at higher risk of dying of drug overdoses, or suicide, or alcoholism. To understand Trump's appeal, and his success, this is a good place to start. Why has a large swath of America seem to have lost hope? And why do they believe that Trump will make their lives better?