People hold conversations through the U.S.- Mexico border fence Saturday at Border Field State Park in San Diego. (Mike Blake/Reuters)

President Trump’s vision of a “big, beautiful” wall along the Mexican border may never be realized, and almost certainly not as a 2,000-mile physical structure spanning sea to sea.

But in a systematic and less visible way, his administration is following a blueprint to reduce the number of foreigners living in the United States those who are undocumented and those here legallyand overhaul the U.S. immigration system for generations to come.

Across agencies and programs, federal officials are wielding executive authority to assemble a bureaucratic wall that could be more effective than any concrete and metal one. While some actions have drawn widespread attention, others have been put in place more quietly.

The administration has moved to slash the number of refugees, accelerate deportations and terminate the provisional residency of more than a million people, among other measures. On Monday, the Department of Homeland Security said nearly 60,000 Haitians allowed to stay in the United States after a devastating 2010 earthquake have until July 2019 to leave or obtain another form of legal status.

“He’s building a virtual wall by his actions and his rhetoric,” said Kevin Appleby, migration policy director for the Center for Migration Studies, a nonprofit think tank.

Trump administration officials say they are simply upholding laws their predecessors did not and preserving American jobs. Previous Republican and Democratic administrations were too soft on enforcement, they say, and too rosy in their view of immigration as an unambiguously positive force.

“For decades, the American people have been begging and pleading with our elected officials for an immigration system that’s lawful and serves the national interest,” Attorney General Jeff Sessions said in Austin last month. “Now we have a president who supports that.”

Bob Dane, executive director of the Federation for American Immigration Reform, which has pushed for many of the Trump administration’s main goals on immigration, said the president has “really scaled back this expansive view of immigration that occurred under the Obama administration.”

The new restrictions could significantly reduce the number of foreign-born workers in the U.S. labor force, but demographic experts say there is little chance they will alter the country's broader racial and ethnic transformation, which Trump's critics say is his goal. Census projections show the United States will no longer have a single racial or ethnic majority by mid-century, according to the Pew Research Center.

Still, by erecting tougher, taller administrative hurdles for foreigners seeking to move to the United States or remain in the country after arriving illegally, the White House is attempting to shift the country back toward the tighter controls on immigration in place before the 1960s.

“Within the administration there are a number of key players who are just looking for every opportunity, every program . . . every administrative or regulatory leeway they have to restrict entry into the United States,” said Linda Hartke, president and chief executive of the Lutheran Immigration and Refugee Service, which resettles refugees.

Even as they fight court orders seeking to halt parts of Trump’s immigration agenda, Sessions, White House senior adviser Stephen Miller and other key players are finding ways to shrink the immigration system. Miller was an aide to Sessions before both men joined the administration; in less than a year, their immigration policy prescriptions have moved from the realm of think-tank wish lists to White House executive orders.

In October, the White House — in a plan led by Miller — said it had conducted a “bottom-up review of all immigration policies” and found “dangerous loopholes, outdated laws, and easily exploited vulnerabilities in our immigration system — current policies that are harming our country and our communities.”

Trump has endorsed GOP legislation to cut annual, legal immigration by half, reducing the number of green cards issued annually from about 1 million to 500,000. More weight would be given to immigrants with job skills, as opposed to those with extended family in the United States.

The president cut the number of refugees the United States is willing to accept annually from 110,000 to 45,000, the lowest level since 1980, and ordered the implementation of a time-consuming “extreme vetting” system that could mean the number of refugees cleared each year is much lower. In October, 1,242 refugees arrived in the United States, down from 9,945 in October 2016.

Trump also eliminated a smaller program specifically for refugees fleeing violence in Central America. The Pentagon, citing concerns about vetting, suspended a recruitment program offering skilled foreigners a fast track to citizenship if they serve in uniform.

Muzaffar Chishti, the director of the Migration Policy Institute at the New York University School of Law, said nearly 350,000 of the newcomers who arrive legally to the United States each year are the spouses and minor children of U.S. citizens and permanent residents. Since barring those arrivals is not under consideration, Chishti said, the government would have to eliminate or sharply restrict almost all other avenues to reduce the annual number of immigrants to 500,000.

In addition to this week's decision on Haitians, the government earlier this month declined to renew Temporary Protected Status, a form of provisional residency, for about 2,500 Nicaraguans. The State Department says conditions in Central America and Haiti that had been used to justify the protection for as long as two decades no longer necessitate a reprieve. Decisions on more than 250,000 Hondurans and Salvadorans with the provisional residency permits are pending.

Trump is also ending Deferred Action for Childhood Arrivals, or DACA, the Obama administration program that granted work permits to 690,000 young immigrants brought here as children. Trump's administration is expanding immigration courts and detention centers and has ratcheted up deportations from the interior of the United States, where millions of undocumented immigrants with U.S.-born children and no serious criminal records held little fear of expulsion under President Barack Obama.

Arrests by Immigration and Customs Enforcement are up more than 40 percent this year, and the agency wants to more than double its staff by 2023, according to a federal contracting notice published this month. ICE is calling for a major increase in workplace raids and has signed more than two dozen agreements with state and local governments that want to help arrest and detain undocumented residents.

“If you’re in this country illegally and you committed a crime by entering this country, you should be uncomfortable,” Thomas Homan, the top official at ICE, told lawmakers this year. “You should look over your shoulder. And you need to be worried.”

The president and his aides have pressed forward despite an outcry from advocates and Democratic lawmakers, who in states such as California and Illinois have instructed police and public officials to shun cooperation with ICE. The Trump administration has threatened to strip such "sanctuary" jurisdictions of federal funding in an escalating legal standoff.

Trump's tough talk alone appears to be one of the administration's best bulwarks: Illegal crossings along the border with Mexico have plunged to their lowest level in 45 years, and U.S. agents are catching a far greater share of those attempting to sneak in. Applications for H-1B skilled visas and new foreign-student enrollment have also declined.

William Frey, a demographer at the Brookings Institution, said that until now U.S. immigration rates have largely spared the country from the challenges facing advanced industrial nations such as Japan and Germany that can’t replace aging workers fast enough. By slashing immigration, Frey said, the country could end up with labor shortages and other workforce issues.

But although some of Trump’s most fervent supporters see curbing immigration as a way to turn back the United States’ rapid racial and ethnic transformation, Frey said it is an unrealistic goal. By 2020, census projections show minorities will account for more than half of the under-18 U.S. population, because of higher birthrates in nonwhite populations. And by 2026, the number of whites is projected to begin declining in absolute numbers, he said, as deaths exceed births.

“You can slow the rate of Latino and Asian immigration, but it won’t make the population whiter,” Frey said. “It will just become less white at a slower pace.”

Trump continues to insist his administration will build a border wall, despite exorbitant cost projections and senior DHS officials saying a 2,000-mile structure is impractical. His supporters say they admire the president for plowing ahead in his overhaul efforts and see a historic, generational shift underway.

“There is more than one way to get to the goal,” Dane said. “Legislative solutions are all great, but clearly the administration has done things behind the scenes. . . . The results have been dramatic.”