After a massive failure of presidential leadership — ignoring preventive measures to contain the spread of the coronavirus, which has both necessitated the unprecedented closure and collapse of the economy and soaring unemployment and contributed to 45,000 American deaths and counting — President Trump returned to the playbook that got him to the White House. On Monday night, he used the pretext of the pandemic to tweet that he intended to suspend immigration to the United States, before announcing further details.

The scope of the policy is hazy, with officials reportedly scrambling to write an executive order giving legal and practical boundaries to the president’s most recent rantings. The president’s tweets often presage real policy change, though what he says doesn’t instantly become law; reporting suggests that the draft executive order may be more narrow than initially touted. Yet by announcing a total moratorium on immigration, he may have incited panic as well as signaling his core values and vision.

Of course immigration is not a vector for the spread of the coronavirus, which is already circulating within the country. And xenophobia only exacerbates the problem in dangerous ways. The president’s rhetoric has already been linked to rising hate crimes and violence against Asian Americans, and continuing to cast foreign-born and nonwhite people as bringers of disease may further fan these flames. A full immigration ban could possibly limit the ability for the United States to recruit needed health-care and agricultural workers or make it impossible for families to reunite at a time when we especially need the people we love.

So why suggest an immigration ban? Because times of crisis create opportunities for anti-immigration advocates to cast blame on outsiders and transform policy in ways they have long sought, to arrest what they perceive as “demographic change" and the loss of a white America. Trump’s emergency measures therefore could outlive his presidency.

As Jews and Catholics from Southern and Eastern Europe overtook protestants as the bulk of immigrants coming to the United States in the early 20th century, nativists, alarmed by the portended demographic change, sought to regulate the race and national origins of immigrants. They believed that Jews, Italians and others, as well as Asian immigrants, were biologically and culturally inferior to Protestants from Northern and Western Europe and they wanted to protect American “whiteness” from “inferior” racial stock.

In the 1920s, nativists won, passing restrictive laws that curtailed immigration with a system of per-country quotas that remained in place for the next 40 years.

In the 1960s, policymakers rejected race-based restrictions to create a more equitable system. But shifting geopolitics led to an unexpected outcome: Over the next decade, immigrants came increasingly from beyond Europe, from Latin America and Asia, and later African countries. Like previous generations of immigrants to the United States, they found some combination of opportunity and discrimination, and poured their talents, gifts and hard work into their communities to create better opportunities for themselves and their children.

But like their predecessors in the early 20th century, nativists in the 1970s bristled at the arrival of these immigrants. As the writer Peter Brimelow would put it, late 20th-century immigration was “Adolf Hitler’s posthumous revenge on America.” Because postwar liberals had been so intent on eliminating racism and xenophobia from U.S. policy, they’d inadvertently enabled immigration that was destroying “the American nation” as Brimelow understood it, that is to say, primarily white and Protestant.

A newly invigorated nativist movement launched from unlikely roots: the environmental movement, with its focus on limiting population growth. John Tanton, with support from a small circle of like-minded thinkers and funders, founded the Federation for American Immigration Reform (FAIR) in 1979. Rather than reintroducing a quota system, Tanton and his fellow reformers believed that they could focus on the numbers and push policymakers to dramatically cut immigration, which would naturally cut immigration of nonwhite people.

Tanton drummed up public support by focusing on unauthorized immigration. Policy changes, notably the end of the Bracero program in 1964, had increased the number of unauthorized immigrants, as people who once came legally now lost their governmental stamp of approval. Yet, Tanton recognized that vilifying these workers as “illegal” would frame the byproduct of this policy shift as an issue of individuals’ immorality and law breaking. He cultivated relationships with stakeholders who cared primarily about this issue, like the Immigration and Naturalization Service and Border Patrol labor union.

But Tanton understood that as long as legal immigration continued, people of color would continue to become Americans. In a 1979 proposal, Tanton and FAIR’s first executive director Roger Conner were clear that its goal would be “to reform policies governing legal immigration, conforming them to today’s demographic, resource, political and social realities.”

Tanton was especially worried about the shift in American demographics, and different birth rates of people of different races. “As our native birthrate falls, immigration will account for an increasing proportion of our growth,” Tanton warned. Later he worried that the present majority, presumably of white Americans, would be overwhelmed by more fertile groups: As he wrote in a 1986 memo, “will the present majority peaceably hand over its political power to a group that is simply more fertile?”

FAIR and the other organizations founded or funded by Tanton, including the Center for Immigration Studies, Immigration Reform Law Institute and NumbersUSA, tended to frame their policy preferences in terms of numbers. They understood well that “restricting” immigration by the numbers instead of “excluding” based on race would achieve their goals and disproportionately limit and exclude the migration of nonwhite people without running afoul of the race-neutral language that tended to fly in Washington.

It almost worked.

In the 1990s, fearmongering about unauthorized immigrants fueled a policy debate about drastically restricting immigration. Proposed provisions to punish undocumented people were uncontroversial. And while even policymakers who supported harsh and punitive laws tended to distinguish that they supported legal immigration, some were swayed by FAIR’s argument that perhaps too many immigrants were being admitted legally and there should be a complete — if temporary — moratorium on legal immigration.

Was the age of American immigration over? It seemed possible; in 1995, the bipartisan Jordan Commission issued a report calling for cuts to annual immigration and the elimination of several categories of family immigration and the Diversity Visa lottery. Republicans controlled Congress, and immigration hard-liners had significant power in the relevant immigration subcommittees.

Yet they didn’t succeed. The resulting 1996 legislation fueled a steep rise in immigrant detention and deportation, ensnaring legal as well as unauthorized immigrants, and creating a system that has left millions of people vulnerable. Additionally, fearmongering that what Brimelow called an “unprecedented demographic mutation” would make Americans “become alien to each other” managed to gain adherents, especially on the far right. It also seeped into a political discourse that treats immigration and demographic change as innately threatening.

But Congress opted not to cut legal immigration. No cuts, no moratorium. FAIR’s proposals to end birthright citizenship also went nowhere.

Until now.

President Trump’s administration has imposed serious restrictions on legal immigration through executive action, without congressional approval. Informed by the Tanton network’s recommendations and proposals, the Trump administration has used executive power to ban travel from specific countries, to reduce the number of refugees resettled, to all but eliminate the right to seek asylum, to cut legal immigration by slowing visa processing and by imposing new regulations making it easier to reject applications from families that have used certain public benefits.

Trump’s latest tweet suggests he hopes to realize Tanton’s vision and cut immigration to zero. He’s even borrowed a page from FAIR and is framing the cut as temporary, which restrictionists realize puts the onus on advocates to restore immigration later, a presumably tough lift in our divided, inert system.

Even if Trump’s tweets are a form of political theater, they come with real costs. This hardening idea about who can be American has nothing to do with keeping Americans safe from the coronavirus. Instead, it will only make all of us more vulnerable as racism and xenophobia thwart support for a humane, comprehensive response to the covid-19 pandemic.