One of the most longstanding hopes (on the left) and fears (on the right) about democratic politics is that voters of modest means will use their electoral weight to level the economic playing field. In a market economy, the median voter's income will invariably be below the national average creating an apparently compelling opportunity for a politics of redistribution. This makes the sustained increase in income inequality in the United States and other developed countries a bit of a puzzle. One common suggestion, offered recently by Eduardo Porter in The New York Times, is ignorance. Voters "don't grasp how deep inequality is."

But while Americans understanding of economic trends is certainly imperfect, the data suggest that the broad trends are known to the population. Nathan Kelly and Peter Enns, for instance, find that when asked to compare the ratio of the highest paid occupation and the lowest, Americans at the bottom of the income distribution do believe inequality is high and rising. In 1987, Americans as reported that the highest-paid occupation took home 20 times what the lowest paid occupation did - by 2000, they thought the gap had grown to 74 times.

A recent Pew survey finds that 65% of adults agree that the gap between the rich and everyone else has increased in the past 10 years, only 8% say it has decreased. A Gallup poll from earlier this year suggests that 67% of Americans report that they are either "somewhat" or "very" dissatisfied with the income and wealth distribution in the U.S.

If ignorance doesn't explain inaction, what does? These five factors are the most important culprits:

1) Upward mobility

According to research from Carina Engelhardt and Andreas Wagner, around the world people overestimate the level of upward mobility in their society.

They find that redistribution is lower then when actual social mobility is but also lower where perceived mobility is higher. Even if voters perceive the level of inequality correctly, their tendency to overstate the level of mobility can undermine support for redistribution. In another study Alberto Alesina and Eliana La Ferrara find that, Americans who believe that American society offers equal opportunity (a mythology) are more likely to oppose redistribution. Using data from 33 democracies, Elvire Guillaud finds that those who believe they have experienced downward mobility in the past decade are 32% more likely to support redistribution. A relatively strong literature now supports this thesis.

2) Inequality undermines solidarity

Enns and Kelly find, rather counterintuitively, that when "inequality in America rises, the public responds with increased conservative sentiment." That is, higher inequality leads to less demand for redistribution. This is perhaps because as society becomes less equal, its members have less in common and find it less congenial to act in solidarity. Bo Rothstein and Eric Uslaner argue that, "the best policy response to growing inequality is to enact universalistic social welfare programs. However, the social strains stemming from increased inequality make it almost impossible to enact such policies."

As inequality increases, the winner-take-all economy leads voters try to look out for their own children. The period during which overall inequality has risen has seen a massive increase in more affluent families' spending on enrichment for their own children.

Chris Dillow points to research by Klaus Abbink, David Masclet and Daniel Mirza who find in social science experiments that disadvantaged groups are more likely to sacrifice their wealth to reduce the wealth of the advantaged group when inequality was lower than when it was higher. Kris-Stella Trump finds that rising inequality perpetuates itself, noting that, "Public ideas of what constitutes fair income inequality are influenced by actual inequality: when inequality changes, opinions regarding what is acceptable change in the same direction."

3) Political misrepresentation

Ideological factors can't tell the whole story. Many Americans support redistributive programs like the minimum wage and support for the idea that hard work leads to success has plummeted in the last decade. A further important reason for the lack of political response to inequality relates to the structure of American political institutions, which fail to translate the desires of less-advantaged Americans for more redistribution into actual policy change. Support for this thesis comes from many corners of the political science field, including Martin Gilens, Dorian Warren, Jacob Hacker, Paul Pierson, and Kay Lehman Schlozman. Research by five political scientists finds that status quo bias of America's often-gridlocked congress serves to entrench inequality.

More simply, lower-income Americans tend to vote at a lower rate. William Franko, Nathan Kelly and Christopher Witko find that states with lower turnout inequality also have lower income inequality. Elsewhere, Franko finds that states with wider turnout gaps between the rich and poor are less likely to pass minimum-wage increases, have weaker anti-predatory-lending policies and have less generous health insurance programs for children in low-income families. Kim Hill, Jan Leighley and Angela Hilton-Andersson find, "an enduring relationship between the degree of mobilization of lower-class voters and the generosity of welfare benefits." Worryingly, Frederick Solt finds that, "citizens of states with greater income inequality are less likely to vote and that income inequality increases income bias in the electorate." That is, as inequality increases, the poor are less likely to turn out, further exacerbating inequality.

4) Interest-group politics

The decline of labor unions has decreased the political importance of poor voters, because unions were an important "get-out-the-vote" machine. A recent study by Jan Leighley and Jonathan Nagler finds that the decline in union strength has reduced low-income and middle-income turnout. But labor's influence (or lack thereof) is also important when the voting is done. Research finds that policy outcomes in the United States are heavily mediated by lobbying between interest groups, so organization matters.

Martin Gilens writes, "Given the fact that most Americans have little independent influence on policy outcomes, interest groups like unions may be the only way to forward their economic interests and preference." His research indicates that unions regularly lobby in favor of policies broadly supported by Americans across the income spectrum, in contrast to business groups, which lobby in favor of policies only supported by the wealthy.

It's no surprise then that numerous studies have linked the decline in union membership and influence with rising inequality.

5) Racial conflict

A recent study by Maureen A. Craig and Jennifer A. Richeson finds that when white Americans are reminded that the nation is becoming more diverse, they become more conservative. Dog-whistle phrases like "welfare queens" have long driven whites to oppose social safety net programs they disproportionately benefit from. Research from Donald Kinder and Cindy Kam indicates that racial bias among white voters is strongly correlated with hostility toward means-tested social assistance programs. Another study by Steven Beckman and Buhong Zhen finds that blacks are more likely to support redistribution even if their incomes are far above average and that poor whites are more likely to oppose redistribution.

In other words, a massive public education campaign about the extent of income inequality is neither necessary nor sufficient to achieve the kind of redistributive policies liberals favor. The real obstacles to policy action on inequality are more deeply ingrained in the structure of American politics, demographics, and interest group coalitions. Insofar as there is a role for better information to play, it likely relates not to inequality but to social mobility which remains widely misperceived and is a potent driver of feelings about the justice of economic policy. As John Steinbeck noted, "Socialism never took root in America because the poor see themselves not as an exploited proletariat but as temporarily embarrassed millionaires." Stronger unions, more lower income voter turnout and policies to reduce the corrupting influence of money on the political process would all work to reduce inequality. It will take political mobilization, not simply voter education to achieve change. The wonks have interpreted the world; the point, however, is to change it.