State and local governments have a huge influence on citizens’ daily lives. They spend people’s tax dollars. They decide how schools operate and what constitutes a crime. And yet, few people seem to care these days. State and local elections aren’t drawing the interest from voters or the media that they did a few decades ago. National politics, on the other hand, is a bit like your smartphone: Even when you know that other things demand your attention, you can’t seem to look away. That’s a worrisome trend, particularly in a federalist system like the one in the United States, which gives state and local officials wide-ranging authority.

How did national politics manage to crowd out state and local politics? I take up that question in my new book, “The Increasingly United States: How and Why Political Behavior Nationalized.” The book considers a wide range of potential causes for and consequences of national politics’ ever-longer shadow, including its relationship with partisan polarization and its impacts on voting. In this article, though, I want to focus on just one part of the broader puzzle: the transformation of our media markets and how that affected voters’ knowledge and participation levels.

Americans today are far more engaged with and knowledgeable about national politics than state or local politics, a gap that has been growing in recent decades. And it turns out that the changing media environment is a key engine of today’s nationalization. More and more, Americans are turning away from the media outlets that are most likely to provide a modicum of state or local coverage. They are substituting Fox News (or maybe FiveThirtyEight) for the Fayetteville Observer, and The New York Times’ website for the Nevada Appeal.

Our increasingly national gaze

It’s not exactly news that turnout for state and local races is lower than turnout for presidential races. But this pattern’s very familiarity may have obscured just how surprising it is. After all, states and localities take primary responsibility for schools, transportation and criminal justice, three policy areas that can have a major effect on people’s day-to-day lives. And if people were motivated to vote primarily by the idea that their vote might decide the outcome, they would be far more likely to cast a ballot in a small local elections, where their odds of being the decisive vote are much higher, than in a national one.

In a federalist system, it is always noteworthy when national politics draw a disproportionate level of attention — and all the more so when the gap between national politics and state and local politics has been growing sharply. That’s exactly what has been happening in the past few decades: Voter turnout for president has remained roughly constant while turnout for state and local races has fallen.

So why have these gaps in turnout and engagement grown? A key part of the answer is right before your eyes. Since 1980, the way in which Americans learn about politics has transformed — and that transformation has given national content providers an advantage over older, spatially bound media sources. A few decades ago, on local TV news or in newspapers arriving at readers’ doorsteps, the media consumer was likely to see a lot of content that was targeted to her based on where she lived. Both advertisers and editors thought about their audiences geographically, and tailored their coverage accordingly.

In recent years, though, our reliance on spatially bound media sources has eroded. Cable television and the internet have introduced a host of new competitors that attract audiences based on a shared interest in politics rather than a shared geography.

Consider the chart below, which uses Pew Research Center surveys to show the share of Americans who report that they regularly use different types of media to get information about politics and how those shares have changed over time.

North of 70 percent of respondents indicated that they were regular newspaper readers as late as 1990, a figure that fell to the high 50s by 2014. The drop in those who reported watching local TV news is even steeper, from above 75 percent to below 50 percent. Over that same period, the share of people who reported getting news online more than tripled, from 15 percent to 46 percent. And while in theory those citizens could be going to the websites of local news outlets, research has found that they emphatically are not, so the shift to online news has meant a shift away from local content, too. Americans are moving away from media outlets that are likely to have some state and local coverage and toward those that do not.

Still, how do we know that these shifts actually contribute to the growing turnout gap? One way to connect the two trends is to look at turnout in media markets that get different levels of local political coverage. We know from prior studies that people who live in the same media market as their state capital have tended to get more information about state-level politics. That makes sense: It’s much cheaper to produce news about state politics from the state capital than from the far corner of the state. Gubernatorial turnout within those media markets also tends to be higher than in other parts of states. So, if citizens are in fact watching less local TV news than they used to and so are becoming less engaged with local politics, we should see gubernatorial turnout in state capital media markets decline in recent years relative to places outside those markets.

And that’s exactly what we see. Looking at the ratio of turnout between gubernatorial and presidential elections, before the 1960s, there isn’t much of difference in turnout for governor’s races in state capital media markets compared to other parts of the state. The reason is simple: Local TV news had yet to proliferate. (Early television programming was overwhelmingly national.) But in the 1970s and 1980s, as more Americans got their political information from local television, the advantage to being in the same media market as one’s state capital grew. More recently, cable TV, satellite TV and the internet have frayed the link between where people live and what news they get — and gubernatorial turnout has dropped as a result.

In November, voters will weigh in on 36 gubernatorial elections and more than 6,000 state legislative seats. In doing so, they will shape public policy on a range of issues, from health care and gun control to marijuana and education. Given the gridlock that has stymied federal policymaking for much of the last decade, it’s a good bet that states and localities will be a major arena for public policy battles in the coming years. And yet, many media outlets compete nationally, and so face strong incentives to focus on national audiences. The result: Many of the voters who do show up to cast ballots for local races will likely do so with an eye toward national politics, and other citizens will sit the elections out entirely.

Matt Garber and Sam Mitchell provided research assistance.