Throughout the negotiations over the future of “Dreamers,” President Trump’s shifting and often contradictory positions have flummoxed leaders in both parties. How the president came down on the terms of any DACA deal seemed to vary by the hour. But no longer: President Trump has said twice now he is prepared to offer a path to citizenship for as many as 1.8 million undocumented immigrants, including the roughly 690,000 currently enrolled in DACA. But while Mr. Trump’s willingness to entertain a path to citizenship represents a welcome departure, the rest of the proposed deal’s terms are deeply troubling.

In exchange for citizenship for Dreamers, President Trump demands not only $25 billion for a border wall but also a dramatic restructuring of the legal immigration system. Not only would there be an end to the diversity visa lottery, but the immigration package would put an end to what the Trump administration has branded “chain migration.” What were previously understood as “family reunification visas” would be restricted to spouses and minor children. No parents, no siblings, not even adult children under the proposal can be included. According to a study by the Cato Institute, the Trump plan could reduce the number of legal immigrants to the United States this year by almost half.

While Mr. Trump’s willingness to entertain a path to citizenship represents a welcome departure, the rest of the proposed deal’s terms are deeply troubling.

Mr. Trump’s proposal represents an almost complete reversal from previous Republican immigration priorities. Republican resistance to a path to citizenship for undocumented residents had been  understood to at least nominally be based on opposition to rewarding law-breaking with immigrant amnesty. It was to counter this position that the Dreamers’ predicament—having been brought to the United States as children—was emphasized.

But while many opposed what they regarded as amnesty for undocumented people, most Republican leaders have long insisted they were not out to significantly reduce legal immigration. It would be unfair to the legal immigrants, many Republicans argued, to let the undocumented “skip the line.”

But now Mr. Trump, with significant Republican support, is proposing cutting the line in half. This policy is popular enough with the ascendant nativist wing of the G.O.P. that they have offered in return for the cutback the long-derided “amnesty.” It is a whiplash-inducing shift in policy goals.

By adding legal immigration to his targets, Mr. Trump has revealed a desire to resist a long-term demographic trend toward a greater diversity. By holding the Dreamers hostage, Mr. Trump believes he can secure his restrictionist policy goals.

For Democrats the choice is now between protecting immigrants who are here already and those who have yet to come. It is an impossible choice.

What was once a question of how to best deal with America’s large undocumented immigrant population has now become a debate about the future of all immigrants, regardless of status. America’s identity as a nation of immigrants is under attack. Against this revived nativism, which now sees even lawful family-based immigration as a threat, the United States’ commitment to remaining what John Winthrop, John F. Kennedy and Ronald Reagan called the “city upon a hill” requires fierce defending.

This article appears in February 19 2018.