Democrats are exultant that President Trump had to reverse his policy of separating immigrant families at the border. And there is good reason to celebrate: The policy was immoral, mean-spirited and unnecessary. But I do wonder whether this episode will prove to be as damaging to the president as liberals think. With this tussle, Trump sent a clear reminder to his supporters of one simple thing — that he is willing to get tough on immigration.

The president’s cruelty made it easy to oppose his policy. But in their delight at the Trump administration’s latest misstep, Democrats may be walking into a trap. The larger question is surely: Should the country enforce its immigration laws or, if circumvented, should we just give up?

According to a U.N. report, last year the United States became the world’s leading destination for asylum seekers, with a 44 percent increase of Central Americans, who made up almost half the total at about 140,000. David Frum suggests in the Atlantic that most of these people are probably coming to escape poverty rather than violence (which has been declining) and that many hope bringing children will help them avoid punishment. That’s why, when asked in 2014 about the tens of thousands of unaccompanied children who had come to the border, Hillary Clinton responded, “We have to send a clear message: Just because your child gets across the border, that doesn’t mean the child gets to stay. We don’t want to send a message that’s contrary to our laws or will encourage more children to make that dangerous journey.”

Immigration has become an issue that passionately motivates a large group of Americans, perhaps like no other. Some of this might be rooted in racism. But it also represents a kind of heightened nationalism. In an era of rampant globalization, people want to believe that they still maintain some sense of stability and control.

Nationalism has been around for centuries, but it is now, in a sense, the last doctrine standing. The great story of the 20th century was the loss of faith. Between the ascendance of science, socialism and secularism, people lost their trust in the dogmas and duties of religion. But this didn’t change the reality that they wanted something they could believe in, something with which they could have a deep, emotional bond.

Nationalism has increasingly become that substitute for many on the right, being endowed with a strong and almost mystical attachment. For many on the left, by contrast, nationalism is more of an irrational affinity for a group of people with whom one shares an arbitrary border. Why should, say, a devout Catholic in New Hampshire feel a closer connection to a radical atheist who lives about 2,500 miles away in California compared with a fellow Catholic a few hundred miles away in Canada? But such has been the power of nationalism that it continues to move people to great acts of courage, loyalty, cruelty and hatred.

Immigration has become the litmus test of nationalism, perhaps because other sources have faded or become politically unmentionable. There was a time when nationalism was deeply intertwined in many corners of the globe with religion or ethnicity. And it would be openly and proudly described in those terms. But as Western societies became more diverse, and as minority groups within them asserted their own identities, it became more difficult to define nationalism by those older ingredients. So what remains? How does one define a nation?

For Americans, political ideas and ideology have always been at the heart. That is why being a communist could be thought of as “un-American.” But beyond ideology, there has also been, even in America, a more emotional conception of the nation. And immigration has become a proxy for that gut feeling — the sense that the country must be able to define itself, choose whom it will allow to come in and privilege its citizens over foreigners.

The solutions to America’s broken immigration system are complicated. But Democrats would do well to remember plain symbolism as well, something Bill Clinton and Barack Obama never forgot, which is why their rhetoric and actions on immigration were often far more centrist than those of many current Democratic leaders.

In politics, people recall a few simple things. To illustrate that point, a pollster in the 1980s once told me a story. A focus group asked a man whom he would vote for, Ronald Reagan or his Democratic opponent, Walter Mondale. “Reagan,” the man said. “Mondale is a communist.” The pollster explained that this wasn’t true. The man replied, “Well, maybe. I’ll still vote for Reagan. One thing I know, no one’s ever thought he was a communist!”

Trump might have lost this round. But no one will ever think he’s soft on illegal immigration.

Read more: