(CNN) Donald Trump has vaulted to the top of the Republican presidential pack with bold assertions -- and few policy details.

The rare exception: his immigration plan.

As president, Trump says he would eject some 11 million undocumented workers from the country. He cites a specific model for his proposal: "Operation Wetback," an aggressive and unprecedented sweep by U.S. Border Patrol agents in the mid-1950s that plucked Mexican laborers from fields and ranches in targeted raids, bused them to detention centers along the border, and ultimately sent many of them deep into the interior of Mexico, some by airlift, others on cargo boats that typically hauled bananas.

During an interview with Jake Tapper that aired Sunday on "State of the Union," Tapper noted that many people recall the 1954 operation as a "shameful chapter in American history."

"Well, some people do, and some people think it was a very effective chapter," Trump replied. "When they brought them back (to Mexico), they removed some, everybody else left," Trump said. "And it was very successful, everyone said. So I mean, that's the way it is. Look, we either have a country, or we don't. If we don't have strong borders, we have a problem."

Trump's assertion that he could replicate that kind of effort as president, however, ignores how much the country has changed since 1954 and the impact that a massive deportation effort would have on the modern U.S. economy, according to interviews with historians who have studied the immigration tactics of the period, a former Border Patrol agent involved in those operations and immigration experts along the Southwest border. These conversations reveal a deeply flawed operation that even at the time failed to achieve its goal of solving America's illegal immigration problem.

While many of Trump's supporters at his rallies say they favor the kind of operation he has proposed, he has few defenders among immigration experts and academics. In interviews, most said that what Trump is proposing would be virtually impossible to achieve without spending hundreds of millions, if not billions of dollars.

Trump has tapped into voter anger with his rhetoric about getting tough on undocumented immigrants, a theme he highlighted in his first political ad. He has cited the operations of the mid-1950s as a defining point in history that illustrates how large-scale dragnets could remove hundreds of thousands of people in an intensive crackdown. Though immigration officials claim that "Operation Wetback" removed about a million people from the country, Trump asserts that it would be logistically feasible to use the same techniques to take away the estimated 11 million.

"We're rounding them up in a very humane way, a very nice way," Trump said when he cited the operation as his touchstone during an interview last fall with CBS' "60 Minutes."

Trump also highlighted the tactics of "Operation Wetback" -- which drew its name from an offensive racial term used to describe Mexicans who swam across the Rio Grande to enter the U.S. -- during the Fox Business debate in November when he refuted a rival's assertion that it would be impossible to remove 11 million people from the United States. The key to the Eisenhower administration's success, Trump said, was moving undocumented immigrants "way south" within Mexico to discourage them from returning.

"They never came back," Trump said. "Dwight Eisenhower.... You don't get nicer. You don't get friendlier."

But even the conservative candidate emerging as the greatest threat to Trump as the first votes near rejects Trump's aggressive approach.

Ted Cruz told Tapper in a recent "State of the Union" interview that the U.S. should catch those who came here illegally through normal law enforcement practices, not through round-ups.

"No, I don't intend to send jackboots to knock on your door and every door in America," Cruz told Tapper. "That's not how we enforce the law for any crime."

Inflated Deportation Numbers?

It is difficult to determine exactly how effective the 1954 operation was in permanently removing undocumented laborers from the U.S. because records from that time are incomplete. But scholars who have studied that period say it is impossible to verify the Border Patrol's claim that more than 1.3 million people were apprehended and left the country in 1954.

At the end of the summer of 1954, said UCLA historian Kelly Lytle Hernandez, the U.S. Border Patrol announced "they had solved the entire undocumented immigration population through this demonstration of incredible police force" by removing more than a million people from the country.

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"The problem is that's not true at all," said Hernandez, the author of "Migra! A History of the U.S. Border Patrol."

In fact, Hernandez said that border patrol line agents—a force of just 1,079 people in 1954—spent the vast majority of their time during the 1954 operation negotiating "back room deals with employers" and growers. Their goal was to force growers to stop using undocumented workers and hire legal Mexican laborers known at that time as "braceros."

The bracero program began in the early 1940s to help the U.S. handle labor shortages in the Southwest during World War II. Under an agreement between the U.S. and Mexico, a defined number of temporary contract laborers from Mexico were permitted to work in the United States, usually for a year, and were guaranteed a certain wage as well as housing and medical services while working in the country.

There were many more applicants from Mexico than jobs, and many growers balked at providing the specified wage, as well as other services that they did not offer to domestic workers like housing. But the bracero program became a magnet for immigrants from Mexico, and many entered the country illegally after they could not obtain a legal slot through the program.

The so-called "Operation Wetback" was intended to curb that illegal migration, and many growers ultimately did comply.

"The one million deportations that are often cited for 1954 are absolutely inaccurate and false," Hernandez said. "A large number of people who were being apprehended during the summer of 1954 -- and prior to that, and after that -- were being apprehended multiple times, not just within a single year, but within a single day."

Documents also show that some of the people counted as being ejected from the country were never even questioned. Some were merely spotted crossing the border back into Mexico and counted as "voluntary departures" by Border Patrol agents.

The number of apprehensions of illegal workers fell precipitously in the years that followed "Operation Wetback" until the 1980s under President Ronald Reagan. Since then, the number of undocumented workers apprehended, removed or returned to their native countries has ebbed and flowed over the years.

There were 1.16 million apprehensions in the 2004 fiscal year, during the presidency of George W. Bush, for example, but that number fell to just over 700,000 in the 2008 fiscal year as Bush was preparing to leave office. Under President Obama in 2014, nearly 500,000 people were apprehended by the Border Patrol and almost all of those apprehensions were along the southwest border.

Doris Meissner, who was Commissioner of the U.S Immigration and Naturalization Service between 1993 and 2000, noted that deportations reached their highest point in history -- more than 438,000 -- under President Obama in 2013. She questioned how the system could handle the numbers of deportations that Trump is talking about without a significant increase in federal spending and substantial changes to the current legal system. Trump has proposed tripling the number of ICE officers to ramp up the number of deportations each year.

"If 400,000 (deportations) is the most the system has been able to produce when it was really working with a hyper focus, then projecting that out to 11 million, you would have substantial costs," said Meissner, who directs immigration policy work at the Washington-based Migration Policy Institute.

The 1954 operation, she added, "was lawless; it was arbitrary; it was based on a lot of xenophobia, and it resulted in sizable large-scale violations of people's rights, including the forced deportation of U.S. citizens."

Trump's spokeswoman did not respond to an email asking for more detail on how the modern day operation would work and how Trump would ensure humane treatment of those expelled from the country.

Tim Kane, an economist at the conservative-leaning Hoover Institution at Stanford University, said Trump's other proposals to limit illegal immigration could have a far greater impact than a massive deportation force.

"You could build a new (deportation) operation, but it would probably fail like the Eisenhower operation failed," Kane said. Trump's proposals for a nationwide e-verify system and enhanced penalties for workers who overstay their visas could be far more effective, he said.

"If Trump were to do that, or attempt it," Kane said, "that would be a game-changer."

Anti-Immigrant Fervor

Though Trump's candidacy has been driven in large part by anti-immigrant fervor within a sector of the Republican Party, polls suggest he will have a far harder time selling an operation in the style of the 1954 raids to the broader electorate—particularly if he intends to win in swing states with significant Latino populations like Colorado. A Pew Research Center poll conducted last year showed that majorities within both the Democratic and Republican parties favor allowing undocumented immigrants to stay in this country so long as they meet certain requirements.

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Trump will certainly face considerable opposition from Latinos and human-rights activists who have vigorously disputed his notion that the 1954 operation was "humane."

Initially during the original "Operation Wetback," some immigrants were airlifted back to Mexico on planes, but that method of transport quickly lost favor with members of Congress because it was prohibitively expensive.

More often undocumented laborers were bused to detention centers and held in cramped quarters, before being loaded onto banana boats in Port Isabel, Texas. They were transported by boatlift at a cost of $8.00 per head, according to Juan Ramon Garcia's definitive study of the program: "Operation Wetback: The Mass Deportation of Mexican Undocumented Workers in 1954."

The boat transports became the biggest controversy of the operation. Over a journey that often took two days, many workers were forced to sleep side by side in the cargo hold of the banana boats in squalid conditions. Sometimes workers stood guard over one another to prevent robberies or assaults within the close quarters.

"When you would sleep in the boat, you were touching people; You would wake up and you couldn't handle the smell, so you would go to the deck," said Gonzalo Alvarado Sr., who was a 16-year-old ranch hand in Fresno when he was swept up and removed from the U.S. as part of Operation Wetback. "It was very dangerous. We made groups of 10 people to sleep. Nine would go to sleep, and one would stay sitting up and watch out for everyone else. The next person to wake up would then keep watch."

When Alvarado's boat arrived in Veracruz, he said, three of his fellow workers were missing; no one had any explanation of what had happened to them.

The boatlift operations back to Mexico ended in September 1956 after seven workers drowned in an apparent attempt to escape, sparking a riot on the vessel known as the Mercurio. There were conflicting reports of what led to the drownings and the riot, according to New York Times accounts of the incident. Congressional investigators later said the boat resembled "an ancient penal ship" and that some 500 Mexican nationals were crammed aboard a boat that was equipped with two lifeboats that could only hold 48 people, according to an August 1956 Times article.

Conditions were not much better as workers made their way home within Mexico. Many of the workers were given 10 pesos -- a small amount that could not come close to covering the fare required to get home -- and a sandwich and told to find their way sometimes hundreds of miles home via cargo trains.

Alvarado disputed Trump's notion that the operation was an acceptable way to treat undocumented workers in this country -- noting that many families were torn apart in the process.

The Bracero program, a camp in South Texas. Some of the one thousand people processed daily at a detention center.



Ted Cruz's immigration reversal "It's not humane," he said. "The people who come here suffer a lot to come here." Speaking directly to Trump in an interview in Spanish at his home in Coachella, California, Alvarado added: "This will never end. People will continue to come.... All the suffering was for my family -- to have them move forward." Alvarado said he became a permanent legal resident in 1985.

Economic Fallout?

A major sweep like this in the modern era would have "massive economic effects" said Josiah McC. Heyman, director of the Center for Interamerican and Border Studies at the University of Texas-El Paso.

"The 1950s was in a period when people were much more closed in.... If this is even attempted, (it's) going to be an instant, gigantic panic," Heyman said, noting that everyone "in the world has a cell phone" -- ensuring that word would spread quickly and many immigrants would flee as the raids got underway.

In some small cities dependent on the labor of undocumented workers, immigration experts predict that 5% or 10% of the workforce could literally vanish. That could lead to unemployment among U.S. workers if businesses are forced to close, Heyman said.

Trump has not addressed the potential economic fallout of a nationwide dragnet, or what his plan would cost. He has also given no explanation of how he would deal with displaced families. He insisted during an NBC interview that he was "going to keep families together, but they have to go."

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Among the questions for Trump, Heyman noted, is how it would be possible to keep families together given that there are an estimated 5.1 million U.S. citizen children with at least one undocumented parent, most of them from Mexican and Central American families.

"A significant portion of the entire child population would suddenly be made orphans," Heyman said. "If we think about the purpose of having a happy, productive, successful, low-crime, and well-integrated young population in the United States, this would be one of the things we would most want to avoid."

Despite the difficulty of deporting some 11 million people, there has also been little attention paid during the 2016 campaign to the backlogged immigration court system.

While modern identity verification systems may ensure that fewer American citizens are accidentally swept up and removed from the country than in the mid-1950s, an operation of the scale Trump has proposed could spark thousands of lawsuits.

Public Will for Massive Deportation Operation

It is difficult to imagine Trump drawing the kind of support for a large-scale deportation operation that the Eisenhower administration was able to muster in the mid-1950s.

In a precursor to the 2016 debate, the Eisenhower administration was responding to public outcry about the perceived costs of services for undocumented workers—namely in places like California's Imperial Valley, where a study had shown that illegal entrants were driving up police, hospital and social services costs.

Eisenhower's Attorney General Herbert Brownell drew up legislative proposals for dealing with illegal immigration and encouraging growers to use legal contract labor, including the braceros. But his proposals went nowhere in Congress, in part because of the power of large growers in the Southwest, who did not want the federal government meddling with their hiring practices.

In early 1954, Brownell charged retired Army General Joseph Swing, the new Commissioner of Immigration, with leading what would be called "Operation Wetback." He had originally hoped to use Army troops stationed along the border, but that idea was quickly quashed -- in part because opponents feared it would harm important relations with the Mexican government.

Swing still planned the operation, however, much like a military campaign with mobile task force teams of Border Patrol agents who would lead targeted raids in certain geographic areas. Extra Border Patrol agents were brought in from their posts in Florida or along the Canadian Border. Congress increased funding to buy more vehicles and planes for immigration enforcement. And the leaders of the campaign sought cooperation and partners in surrounding communities, particularly among Mexican-American citizens -- and unfurled a massive media campaign to win public approval for the operation.

After a few months, Swing and his colleagues declared that more than a million undocumented immigrants had been removed or had gone back to Mexico voluntarily—branding the operation a "tremendous success."

Mexican-Americans largely cooperated with the Border Patrol during that time —persuaded by arguments that ejecting all of the undocumented workers would improve their well-being and assimilation into the American economy.

It didn't, however, Hernandez said. "And that was a lesson learned."