Among the many things we’ve learned so far in the presidential campaign is this: The Democratic candidates are talking more honestly about health care than about immigration. To develop a coherent approach to immigration in an era of rising asylum claims, Democrats need to explain—among other things—whom they would and wouldn’t let in. But Donald Trump has made that discussion extraordinarily difficult. In the shadow of his brutal policies and bigoted appeals, Democrats are wary of spelling out whom they would deport. That has led to a debate that’s evasive and vague.

On health care, by contrast, the Democratic presidential candidates are happier to delve into detail and express diverging views. Consider how the discussion about Medicare for All unfolded at last week’s debates. During the first debate, the moderator Lester Holt asked the candidates who “would abolish their private health insurance in favor of a government-run plan” to raise their hands. Elizabeth Warren and Bill de Blasio put theirs up, and that sparked a discussion that exposed the contrasting ways in which the Democratic contenders see private insurance.

Although they support letting more Americans buy into Medicare, the more moderate candidates in the first debate, including Beto O’Rourke, described private insurance as effective for some Americans. That argument continued into the second debate. Bernie Sanders insisted that Americans “don’t like their private-insurance companies” and promised to end the insurers’ “greed.” By contrast, Joe Biden emphasized the value of allowing people to choose between keeping their current private insurance and buying into a “Medicare-like plan.” Pete Buttigieg noted, “Even in countries that have outright socialized medicine, like England”—the countries whose health-care systems Sanders and Warren admire—“there’s still a private sector.” Viewers could fairly conclude that, among the party’s leading candidates, there are fundamental differences of opinion about how to structure the health-care system.

But last week’s debates were less successful in clarifying how the Democrats differ on immigration. To be sure, the candidates offered policy proposals: They called for restoring DACA, reforming Immigration and Customs Enforcement, eliminating private detention centers, and giving undocumented immigrants health care and a path to citizenship. In the first debate, Julián Castro also declared his support for downgrading illegally crossing the border from a criminal to a civil offense, and then slammed Beto O’Rourke for disagreeing with him. But while O’Rourke has in the past argued against decriminalization, he wouldn’t defend that position onstage, and instead said he opposed criminalizing asylum seekers, thus evading Castro’s broader point. He was willing to play the centrist on health care, just not on immigration.

In the second debate, the moderator José Diaz-Balart asked for a show of hands on decriminalization. Eight candidates raised their hands; Biden—oddly—raised a finger. But the moderators didn’t ask him to explain. So while viewers were left with a sense that the presidential candidates have different views on decriminalization, they learned nothing about why.

Even more important, the candidates didn’t define the criteria that should govern who gets asylum. That’s significant, because over the past few years, the kinds of people crossing America’s southern border without immigration papers have radically changed. A decade ago, the undocumented were mostly single Mexicans trying to evade capture. Now they’re mostly Central Americans who turn themselves over to Border Patrol so they can apply for asylum. This shift has overwhelmed the asylum process. Cases now regularly take five years to be resolved.

At the debates, Democrats bellowed their opposition to Trump’s handling of the asylum crisis. And they rightly emphasized the need to help Honduras, Guatemala, and El Salvador battle crime, corruption, and poverty so that fewer of their citizens make the perilous journey north. Although they didn’t say so at the debates, the three candidates who have issued immigration plans—Castro,O’Rourke, and Jay Inslee—have also proposed pouring money into the asylum system so asylum seekers can get lawyers and interpreters, and a faster resolution of their claims.

This all makes sense. But it also raises an uncomfortable question. As Bloomberg’s James Gibney has noted, one of the internationally accepted legal criteria for who deserves asylum—fear based on “membership of a particular social group”—is extremely vague. Different immigration judges interpret it in vastly different ways. Since those judges currently work for the attorney general, and thus ultimately for the president, the Democratic candidates need to clarify what standard they support. The easier they make it for asylum seekers to qualify—and the more successful they are in making the process faster and fairer—the more asylum seekers are likely to come. Eventually, improving conditions in Central America may stem the flow. But as Fareed Zakaria has pointed out, the number of asylum seekers from Honduras, Guatemala, and El Salvador has risen in recent years even as murder rates in those countries have dropped.

The point is that there’s a trade-off. Make getting asylum easier, and you’re likely to increase the number of people who apply. When a surge of migrant children reached the U.S. border in 2014, the Obama administration answered that trade-off with a harsh message to desperate Central Americans: “Don’t come. And if you think you’re coming and once you’re here you won’t be returned, that’s not the case. You’re not going to be able to stay.” But in the Trump era, Democrats aren’t comfortable talking that way anymore. Private health insurance is something many Democratic presidential candidates are happy to support openly. Sending vulnerable mothers and children back to Honduras is not.

The moderators should have forced the question. Instead they let the candidates get away with vague calls to “honor asylum claims” (Castro), “follow our own asylum laws” (O’Rourke), “reform how we treat asylum seekers” (Kirsten Gillibrand), and “put in place a meaningful process for reviewing the cases for asylum” (Kamala Harris).

That’s too bad. In addition to condemning Trump’s immoral policies, Democratic candidates need to openly confront the hard trade-offs that the asylum crisis poses. They need to do so to let primary voters make an informed choice. And they need to do so before Donald Trump launches an onslaught of nativist attacks next year. The 2020 Democratic candidates don’t actually support open borders. They’re just not yet comfortable explaining why.