IN SUMMARY, the presence or absence of external danger has always had a profound impact on American domestic politics. Eras of threat are characterized by American unity and consensus; but conformity is stifling and dissent is not tolerated. Eras of safety are characterized by the acceptance of radical and self-critical perspectives, but there is a strong sense of fractiousness as well as uncertainty about America’s role in the world. Oftentimes, outside danger is only noticed in American politics when the menace is present. But the absence of threat is also a fundamental dynamic.

Today, the United States exhibits the classic traits of an era of safety. People are restless, divided, partisan, distrustful of institutions, unsure of America’s identity and role in the world, and skeptical about the use of force. They want to focus on domestic issues, or carry out “nation building at home” as Obama put it. At the same time, there is an acceptance of diverse and even radical political views, and a willingness to question whether the country is on the right path. The Clinton versus Trump campaign is precisely what politics can look like in an era of low threats, with little agreement on foreign policy, and a bitter and even scornful tone.

What’s the solution? We should not yearn for an enemy to arise, or still less, follow the secretary of state’s advice in 1861 and deliberately create one. Eras of foreign danger threaten the lives of Americans, centralize power and undermine the rights of people associated with the danger. Oftentimes, discord is a good thing. The Cold War consensus of the 1950s might have appeared harmonious, but important social problems were swept under the rug.

Instead, presidents have to unify the country the hard way—without a powerful external danger. One answer is to rally people around a positive project like sending a man to the moon. The problem is that threats are more effective unifiers than opportunities. “The British are coming” has greater impetus than “let’s find a cure for cancer.” Indeed, in the 1960s, public support for space exploration was only lukewarm, and this backing was driven in large part by the desire to beat the Russians. Global warming might qualify as a genuine threat to the United States, but it is unlikely to bring Americans together. Psychologists have found that people are more motivated by dangers where there is a responsible agent (like the Soviet Union) rather than impersonal dangers (like global warming).

The effects of threat and safety on domestic politics are not easily overcome. A certain amount of dissension is the price of security. But presidents can dampen down antagonisms and challenge those who seek to divide Americans. At the same time, the White House can offer a positive agenda that is bold, emotionally resonant and appeals to the idealism of Americans—for example, enabling a new era of social mobility.

Americans live in a fortunate, if fractious, era. Sooner or later, they will find themselves confronting a gravely threatening evil, and enviously recall this age of security. Americans need something to fight for—before they find someone to fight against.

Dominic Tierney is associate professor of political science at Swarthmore College, a contributing editor at the Atlantic and a senior fellow at the Foreign Policy Research Institute. His most recent book is The Right Way to Lose a War: America in an Age of Unwinnable Conflicts.

Image: An F/A-18E Super Hornet aircraft on the flight deck of the aircraft carrier USS Harry S. Truman. Flickr/U.S. Department of Defense