There are a lot of things you can say about the Donald Trump administration’s recently announced deportation plan. You can say it is cruel, a policy that could only come from a president who lacks a heart. You can say it has more to do with President Trump’s fevered imagination than the reality of the immigrant presence in the United States. You can say that it’s counterproductive, likely to uproot the very people America should embrace — people who have struggled to get to the US with the goal of working hard and making a better life for themselves and their children.

But if Trump is able to get the money from Congress to hire the 10,000 additional immigration cops and 5,000 more border agents he wants, if he gets local sheriff’s departments to help the federal government round up undocumented immigrants, and if he does indeed begin to deport hundreds of thousands, and perhaps millions, of them, then I think you’ll be able to say something else about his policy: It will be economic suicide.

In 2014, the latest year for which numbers are available, there were 11.1 million undocumented immigrants in the US, according to the Pew Research Center. That’s down from a peak of 12.2 million in 2007. The numbers have shrunk primarily because Mexicans are no longer coming over the border in the numbers that they used to. As of 2014, there were 5.8 million undocumented Mexicans in the US, compared to 6.9 million in 2007. There are a lot of reasons for the decline, not least the upsurge of good jobs in Mexico that have resulted from the North American Free Trade Agreement. But that decline has had a pronounced effect on any number of US industries that rely on manual labour: Farms, building construction and factories among them.

“We’re really near full employment, and are likely facing a tight labour market for the next decade or so,” said Donald Grimes, a senior research specialist at the University of Michigan. “The only place firms are going to be able to find workers will be migrants.”

Frank Gasperini, the president and chief executive of the National Council of Agricultural Employers, told me that of the 1.5 million seasonal agricultural workers, somewhere between 50 and 80 per cent are immigrants, depending on who’s counting. With the labour market so tight, he said, many farms are as much as 50 per cent short of the workforce they need. Farmers have adapted by planting fewer acres with only the most high-margin crops, like grapes and almonds. Less profitable crops, like olives, have been pared back. (The California drought has also influenced these decisions.)

Gasperini insists that farmers don’t purposely hire undocumented workers, but c’mon. They certainly know that many of their workers are in the US illegally — and that a wholesale effort by the government to round them up and send them back would be devastating. Native-born citizens, Gasperini said, simply don’t want to pick crops, so farmers would have to either plant fewer acres or pay significantly higher wages to lure legal immigrants. The result would be two-fold: Higher prices at the grocery store and an increase in imported fruit and vegetables. Oh, and what country would most likely be exporting those fruit and vegetables to the US? Mexico. Somehow, I don’t think that’s the result Trump has in mind.

The building trades, which also rely on immigrants, have much the same problem: Not enough workers for too much work. As David Brooks pointed out in the New York Times recently, the shortage of workers means that projects aren’t being started, which means “less home-buying, less furniture-buying, less economic activity”.

And then there are American factories. “Trump says he wants to bring back manufacturing,” said Dov Charney, “But you can’t manufacture without immigrant labour.” Charney, I realise, is something of a flawed spokesman. In 2014, he was forced out of American Apparel, the clothing company he founded more than two decades earlier, the result of sexual harassment charges and a string of unprofitable quarters. But Charney was one of the few clothing manufacturers to locate his factories in the US, which he insists can be done profitably.

“You are not going to have a ‘Made in America’ manufacturing resurgence with native Americans,” he said. Again, it is not the kind of work most American-born citizens want to do — even though Charney offered decent wages and benefits. “It is the motivated immigrant you need,” he added. “I employed thousands of immigrants. The secret of American Apparel was that very few of our workers were Americans.”

For years, Charney hired undocumented workers — but, as Nicole Gelinas noted recently in the New York Post, a federal inspection in 2009 forced him to fire 1,500 workers, making it even more difficult for him to find employees. “The country doesn’t support manufacturing,” Gelinas concluded. Charney would agree. If Trump really hopes to revive manufacturers, kicking out immigrants is just about the dumbest policy he could devise.

There are other issues, too. In many parts of the country, the population is stagnating — except among immigrants. According to Grimes, between 2006 and 2015, US-born citizens in the prime working ages of 24 to 54 declined to 102.3 million from 104.5 million. During that same nine years, immigrants in the same age group — both legal and illegal — rose to 25.3 million from 22.6 million. The US economy is going to need every one of those workers.

Finally, if America gets a reputation for being hostile to immigrants — or if the Trump administration pares back the various routes to legal immigration — it may well scare off the highly-educated, highly-skilled immigrants who have, for instance, helped make Silicon Valley such a font of innovation. No more Sergey Brins. No more Andy Groves. No more Elon Musks.

The point is: America doesn’t need fewer undocumented immigrants. It needs more of them. The economy depends on it.

— Bloomberg

Joe Nocera is a Bloomberg View columnist.