Income inequality has fueled much of the political debate in the US over the past year. The presidential campaigns of Bernie Sanders and Donald Trump in particular have capitalized on the dissatisfaction of white working-class Americans—defined here, broadly speaking, as men and women with less than a college degree.

It’s well established that working-class Americans of all races have borne the brunt of the economic slowdown that the US has experienced since the late 1970s. But in 2015, an economic study I co-authored with Angus Deaton found that white working-class Americans are also increasingly dying from suicide, alcohol and drugs. Their physical and mental distress may be creating a less obvious, yet powerful, wind in the sails of Trump and Sanders this political season.

The economic disadvantages experienced by less-educated people are clear. The Bureau of Labor Statistics reports that median wages for people with at least a college degree were 80% higher than those with a high school degree in 2014. Private-industry workers with incomes in the top 25% were twice as likely to have access to a retirement plan—and nearly three times as likely to have health benefits—as workers in the bottom 25%.

Differences in education are also associated with marked differences in mortality. For half a century, the mortality rates of white middle-aged Americans (people between ages 45-54) fell by about 2% a year. But starting in the late 1990s, their mortality rates began to rise. Mortality rates in this group have continued to increase through 2014, driven primarily by the deaths of men and women with a high school degree or less.

The biggest factors behind the uptick in mortality among white middle-aged Americans are so-called “deaths of despair”: deaths by suicide, accidental drug overdose, alcoholic liver disease and cirrhosis. Increases in deaths of despair have been large enough to outweigh the progress made in reducing mortality rates from cancer and heart disease, the two biggest killers of middle-aged people.

Rates of death by drug overdose and suicide rose for all white middle-aged people, regardless of education. But the increases were particularly high for those whose education stopped at or before graduating high school.

In 1999, for example, people in this group died from accidental drug and alcohol poisonings at four times the rate of Americans with a bachelor’s degree or more. By 2013, they were dying at seven times the rate of their better-educated peers. In 2013, they also committed suicide at more than twice the rate of people with more education, and died from alcoholic liver disease and cirrhosis at five times the rate of those with a college degree.

Is there a link between the economic decline of the working class and increasing deaths from alcohol, drugs and suicide? And does rising economic inequality play a role in the increasing disparity among those who die from deaths of despair? At this point, we can only speculate.

However, it’s worth noting that while lower-skilled jobs have also declined in European nations, these countries have not experienced a parallel rise in deaths among middle-aged people. European countries have better social safety nets than the US, and workers with less education may be better protected by European social policies.

European countries have also been more reluctant than the US to embrace prescribing potentially addictive painkillers. In the US, meanwhile, drug policy and social policy are driven by a new kind of golden rule: he who has the gold makes the rules.

As the gold becomes more highly concentrated among the wealthiest US citizens, policies that protect the working class have become harder to pass. Trump and Sanders have very different ideas about what helping lower-income Americans might look like. But it’s clear that many white Americans in that demographic feel that they are in crisis—and that the candidates, seeking to harness what is a substantial voting bloc heading into 2016, are shaping their campaign platforms around an audience that feels increasingly invisible.