Area high school students, working for the Student Conservation Association are helping to rehabilitate and construct trails at the Manassas National Battlefield. (Margaret Thomas/The Washington Post)

Stan McChrystal, a retired U.S. Army general and former commander of U.S. and international forces in Afghanistan, is chairman of the leadership council of the Franklin Project on national service at the Aspen Institute and co-founder of McChrystal Group.

This month Americans chose many new leaders, but they continue to have diminished faith in the system in which those leaders serve. Over the past few elections, American politics has produced a succession of dramatic victories and defeats but not a sense of common national purpose. Trust in government is near all-time lows, and social trust — trust in others — is lower among millennials than previous generations. A change in elected leaders has not healed the divisions of our nation, because the problem runs deeper than politics.

The leaders we elect are not succeeding, in part because they reflect us. Just as they have grown less likely to cross the aisle to get things done, we as citizens have become less likely to have a sense of common identity or experience. Turnout for the recent election was the lowest for a midterm in more than 70 years. We are increasingly likely to live among, befriend and work with people with views and backgrounds similar to our own. We have sustained a series of wars for more than 13 years with less than 1 percent of the population serving in the military, creating a gap in experience and understanding between those who serve and those who do not. We lack common experiences that bind us as a people. We have lost our confidence in doing big things as a nation.

Citizenship is like a muscle that can atrophy from too little use; if we want to strengthen it, we need to exercise it. We need to support leaders who ask more of us and not those who simply promise us more. We need candidates who will cross the aisle in support of a big idea for renewed citizenship.

Two years from now, the United States needs to have an election — and a corresponding public campaign — that asks more from us as citizens. As someone who spent 34 years in the military, I have no interest in partisan politics. But informed by my service, I am concerned about a dangerous gap I see in American life: a gap of shared experience, common purpose and gratitude.

So today I’m calling on voters, donors and future candidates to work together to make a “service year” a common expectation and opportunity for all 18- to 28-year-old Americans. This would be an American version of universal national service — appropriately voluntary but socially expected. Through such service, young Americans from different income levels, races, ethnicities, political affiliations and religious beliefs could learn to work together to get things done. Such a project should be a defining issue of the 2016 election.

It is no longer enough for our politics to focus on what is comfortable and convenient; that will only encourage further cynicism and division. If we demand what is needed and what is right, we can reshape the political debate. Our country and our citizens have responded to this type of call before — including the generation of military men and women who volunteered after the 9/11 attacks, many of whom I was proud to command. Our nation has never preferred what is easy when it mattered most. Americans have tried, imperfectly at times, to embrace big goals and to make sacrifices on behalf of the future.

Many people already serve, whether in the State Department, in the military, in the Peace Corps or AmeriCorps, as elected officials, as teachers or firefighters, or in an array of other public-service positions. Demand for national service is high, with more than five times as many applications submitted for AmeriCorps positions as there are opportunities.

What we need is a system of national service that goes well beyond anything that exists today. Every young adult should be called to year-long service, whether as a tutor or mentor in one of our country’s 2.3 million classrooms, a conservation worker in one of our country’s national parks or wilderness areas , an aide to one of the 1.5 million Americans who require hospice care each year or in one of numerous other areas of high unmet need. Such service should provide a moderate stipend to ensure that people from any background could participate, count for some sort of course credit in college and be designed to help make it easier for a service member to get a job.

If candidates ask voters to support this big idea, I know that they will find millions who want to answer the call. Donors who insist their candidates support such an idea will be giving something big back to their country beyond their financial contributions. Voters who support such an idea will be electing candidates who ask them to move beyond an easy citizenship.

Imagine if, during the next election season, candidates at all levels competed to propose serious ideas for the civic transformation of America. Afterward, our newly elected leaders would possess a mandate to converge on a unique patch of common ground. And there is no better common ground than the common experience of serving our country.