Ilya Somin is a law professor at George Mason University, an adjunct scholar at the Cato Institute, and author of "Democracy and Political Ignorance: Why Smaller Government is Smarter." The views expressed are the writers' own.

(CNN) A specter is haunting this year's presidential election: political ignorance. Both Democrats and Republicans love to accuse the other party's supporters of that sin. Sadly, both are often right.

The presumptive GOP nominee Donald Trump has raised exploitation of ignorance to new heights. Many of the main themes of his campaign prey on it. Trump's campaign first took off when he claimed we are being inundated with Mexican immigrants, who increase the crime rate because many are "criminals" and "rapists." In reality, net migration from Mexico has been close to zero for the last 10 years. Yet few Americans seem to know that. And while studies consistently find that immigrants have lower crime rates than native-born Americans, a 2015 Pew Research Center study found that 50% of Americans (and 71% of Republicans) believe immigration is making crime "worse."

Trump's claim that nations such as China, Mexico and Japan are " killing us on trade " because we have trade deficits with them also relies on ignorance. As economists across the political spectrum recognize, free trade benefits the economy, and a bilateral trade deficit between two nations is no more an indicator of economic failure than is my trade deficit with my local supermarket. Unfortunately, studies show that trade is one of the areas where there is the greatest gap between general public opinion and informed opinion.

Trump is far from the only candidate to exploit ignorance this year, merely the most successful. Bernie Sanders, the "democratic socialist" who has mounted an unexpectedly strong challenge for the Democratic nomination, shares some of Trump's demagoguery on trade.

Like Trump, Sanders has also put forward budget projections that most experts, even in his own party , regard as fantastical. Surveys consistently show that most Americans greatly underestimate the percentage of federal spending devoted to big entitlement programs, such as Medicare and Social Security, which are among the largest areas of federal spending. As a result, many voters accept Trump and Sanders' claims that we can not only deal with our serious fiscal problems without reforming them, but also pile on enormous spending increases (Sanders) or tax cuts (Trump). A survey of Sanders supporters by Vox found that the vast majority are unwilling to pay more than a fraction of the tax increases that even Sanders' own projections say would be required to fund the new health care and education programs he proposes. Most likely do not realize the true cost.

The problem of ill-informed voters is certainly not confined to Trump and Sanders, or to the 2016 election; more conventional politicians often manipulate ignorance, as well. It is also not limited to specific issues, instead extending to the basic structure of government.

An October Farleigh Dickinson survey found that only 34% of Americans can name the three branches of government, and 30% cannot even name one. Studies routinely find that large numbers of voters do not know which officials are responsible for which issues, a circumstance that makes it hard to hold them accountable for their performance. All too often, voters reward and punish incumbents for outcomes they do not control, including such things as droughts and even victories by local sports teams.

The biggest determinant of most electoral outcomes is the very recent performance of the economy, even though experts recognize that incumbents usually have little control over short-term economic trends. Such ignorance weakens political accountability, and incentivizes politicians to pursue dangerously misguided policies that prove popular with poorly informed voters.

What is behind this public ignorance?

It is not that the voters are dumb, but that they have little incentive to learn. Because there is only an infinitesimally small chance that any one vote can influence the result of an election, even most smart people usually have little motivation to follow politics closely. That helps explain why political knowledge levels have remained low for decades, in spite of rising IQ scores and educational attainment, and despite the increasing availability of information on the Internet.

There is no easy solution to the problem of political ignorance. But we can at least mitigate it by limiting and decentralizing government. If you are like most people, you probably spend more time considering information when you decide what smartphone to buy than when you decide who to support for president. Similarly, people are far more discerning when they "vote with their feet" to decide what state or local government to live under than when they vote at the ballot box. That is because they realize that individual foot voting decisions are actually likely to make a difference, whereas individual ballots are not.

Devolving more issues to the private sector or to the state and local level can enable us to make more of our decisions in a setting where we have strong incentives to be well-informed. Although it is easy to think otherwise in the year of Trump, most of the public is not stupid. They just need better incentives to make smart choices.