Liberals in Congress wanted to scrap the restrictive quota-based system that had governed U.S. immigration policy for decades. Conservatives feared that America's ethnic and racial composition would be forever transformed.
So in 1965 they compromised: an immigration model that would favor "family unification." By giving priority to the relatives of U.S. citizens, who were mostly of white, European descent, the Immigration and Nationality Act would ensure that future newcomers were overwhelmingly white and European, too.
It did not work out that way. But although the family unification model went on to enjoy broad support as a source of economic and social stability for immigrants, under President Trump it has earned a pejorative label as the enabler of "chain migration."
Ahead of a meeting Wednesday between congressional leaders and White House staffers to discuss the administration's immigration agenda, Trump said that ending "horrible chain migration" will be a condition of any deal that may protect those facing deportation after the Deferred Action for Childhood Arrivals (DACA) program expires starting in March.
"The Democrats have been told, and fully understand, that there can be no DACA without the desperately needed WALL at the Southern Border and an END to the horrible Chain Migration & ridiculous Lottery System of Immigration etc.," Trump tweeted Dec. 29. "We must protect our Country at all cost!"
Attorney General Jeff Sessions, Homeland Security Secretary Kirstjen Nielsen and other Trump Cabinet members have also hammered at "chain migration" in recent weeks, calling it a threat to American workers and national security.
They cite the Dec. 11 failed bombing attack on the New York subway by Bangladesh-born Akayed Ullah, who Trump said "entered our country through extended-family chain migration."
Although the term "chain migration" is not a precise technical one, the White House launched a campaign last month with a slide show offering its own dictionary-style definition: "The process by which foreign nationals permanently resettle within the U.S. and subsequently bring over their foreign relatives, who then have the opportunity to bring over their foreign relatives, and so on until entire extended families are resettled in the country."
Trump has endorsed a bill sponsored by Sen. David Perdue (R-Ga.) and Sen. Tom Cotton (R-Ark.) called the RAISE Act, which would limit visa sponsorship to spouses and minor children of U.S. citizens while implementing a Canadian-style point-based merit system to prioritize skilled workers.
But of the nearly 1.2 million green cards issued during the government's 2016 fiscal year, only about 240,000 went to the type of extended-family visa categories that the legislation would eliminate.
Democrats are unlikely to give ground. Critics see the attack on the family-based system as part of a broader attempt to slow the country's transformation into a more diverse society whose growing rolls of nonwhite voters lean toward the Democratic Party.
They also point out that the diagrams often used to attack "chain migration" — showing a single immigrant bringing dozens of relatives to the United States — hardly reflect the reality of a system that does not move fast enough to allow exponential visa-sponsoring of this sort.
Under the family unification model, U.S. citizens and some legal residents can bring their spouses and minor children relatively easily. But other categories of family members take far longer. An American citizen trying to sponsor a brother or sister from Mexico or the Philippines faces wait times of 20 years or more, because the number of visas that can be issued in the sibling category has an annual cap.
Less important than the numbers, said Francis Cissna, director of U.S. Citizenship and Immigration Services, is the principle that "chain migration" fills the pool of would-be immigrants with candidates whose top qualification is a genetic one, not a job skill.
"One thing is family-based migration, which this administration is not opposed to," Cissna said in an interview. "The problematic part is extended-family-based migration."
An irony of Trump's campaign against "chain migration" is that the liberal reformers of the 1960s wanted a merit-based model, too.
The restrictive immigration quota system established in the 1920s came during a period of heightened anxiety about mass migration from eastern and southern Europe. The quotas limited newcomers from those regions while almost entirely shutting out migrants from Asia, Latin America and elsewhere.
But by the 1960s, the United States was locked in a global ideological struggle against communism, and its quota system had become a stain on America's global image, said Daniel Tichenor, author of "Dividing Lines: The Politics of Immigration Control in America."
"You had Truman, Eisenhower and other prominent national security, foreign policy leaders saying this is crazy, we have people escaping from behind the Iron Curtain who want a haven in the United States, and it helps our national security to welcome them here," said Tichenor, a political scientist at the University of Oregon.
"Just like Jim Crow and the suppression of African American voters embarrassed us abroad, our immigration policies were so blatantly racist it really hurt the world's perception of the U.S. as a global leader and democracy to be emulated," he said.
President Lyndon B. Johnson called for an end to the quota system in his first State of the Union speech in 1964. "In establishing preferences, a nation that was built by the immigrants of all lands can ask those who now seek admission: 'What can you do for our country?' " Johnson told Congress, echoing his slain predecessor. "But we should not be asking: 'In what country were you born?' "
Conservatives, especially the Southern Democrats who opposed Johnson's civil rights legislation and Great Society agenda, were set against the immigration overhaul. But Rep. Michael Feighan (D-Ohio), a longtime immigration hard-liner, devised the family unification model as a compromise to preserve America's ethnic status quo.
"The idea was that you wouldn't get many Asians or Africans coming in because they didn't have relatives here," said Tom Gjelten, an NPR correspondent and author of "A Nation of Nations: A Great American Immigration Story."
At the signing ceremony, Johnson sat at a desk placed in the shadow of the Statue of Liberty.
No other piece of legislation has arguably played a greater role in the demographic transformation of the United States in the decades since.
A backlash against the 1965 act had been building, but Trump's election win supercharged it. The marriage of "chain migration" to Trump's demands for a border wall makes it hard for critics to see the arguments in technical, not racial, terms.
Madeline Hsu, an immigration scholar at the University of Texas, said campaigns to curb legal immigration have been vehicles for what she called "masked racial discourse" and a fear that "the kinds of people coming in or gaining citizenship are racially not the right kinds of people."
Today the United States issues more than 1 million green cards each year, and only about 8 percent go to European nationals. About two-thirds of green cards go to family members of U.S. citizens and legal residents.
"Before, there was a bipartisan view that immigration was good for society and the economy and integral to the history of the United States," said Sarah Pierce, a policy analyst at the Migration Policy Institute, a Washington think tank that is critical of the Trump administration. "But this administration has radically changed the debate."
"While the idea of reducing legal immigration isn't a new one, it was more fringe until now," she said.
Organizations that have long pushed to restrict legal immigration to the United States are enjoying unprecedented influence at the Trump White House, and they push back at charges of ulterior ethnic or racial motives.
A merit-based system probably would bring far more immigrants from China and India, said Matthew O'Brien, director of research at the Federation for American Immigration Reform, a Washington think tank.
"We're cutting out huge numbers of people that have skills and a demonstrated potential," O'Brien said. "And meanwhile we're admitting people simply because they are the extended family of someone who happened to have immigrated previously."