"I'M A huge fan of the Mexican people," Donald Trump said in an interview this weekend with NBC's Chuck Todd. "But they have to pay for the wall." Mr Trump, a real-estate mogul and the current front-runner in the race for the Republican presidential nomination, is such a fan of Mexicans that, in addition to promising to bully them into paying for a pharaonic American infrastructure project, accusing them of mooching off American taxpayers, and blaming them for low wages, unemployment and violent crime, he also proposes to amend the constitution to do away with birthright citizenship, so that children born inside America's borders will no longer be automatic citizens. He would make it harder for Mexicans to come to America lawfully and relentlessly deport those in the country without papers. In short, a huge fan.

In a new, six-page position paper on immigration reform, Mr Trump contends that "the Mexican government has taken the United States to the cleaners" by "exporting crime and poverty", which is alleged to have cost hundreds of billions in tax dollars, to have hurt Americans workers and to have precipitated a wave of murder and mayhem. Meanwhile, billions of American dollars pour into Mexico, sent home by unauthorised workers. Mexicans have made a mess in America, Mr Trump says, "and they must pay to clean it up". Until Mexico ponies up for a wall, Mr Trump proposes to impound remittance payments to Mexico and jack up fees on Mexicans passing legally into the country and on Mexican goods arriving at American ports. More serious trade barriers are not ruled out.

The plan, entitled "Immigration reform that will make America great again", is heavy on populist xenophobia, nationalism and protectionism and exceedingly light on intellectual credibility.

Mr Trump remains in the bad habit of telling lurid stories about immigrant crime, as though they are illustrative of an alarming trend. But as we pointed out in June, over the last thirty years America has experienced a boom in Mexican immigration together with a precipitous drop in violent crime. Mr Trump's rhetoric might lead you to think that the gutters of El Paso, Texas, a border city that teems with Mexican immigrants, must run with blood. Instead, El Paso's murder rate is among the lowest in the country for cities over half a million. Other cities rich with Mexicans, with and without papers, are similarly pacific. Mr Trump seems to be encouraging distress over a total non-problem in order to win respect for his courageous determination to take it on.

A special report on America's Hispanics Mr Trump's white paper also misleads about the economic and fiscal effects of illegal Mexicans, inflating the costs while ignoring benefits. "The effects on jobseekers have been disastrous", Mr Trump claims. Yet labour economists routinely find that immigrants have done little or nothing to push down wages or force native workers out of jobs. According to Gianmarco Ottaviano, Giovanni Peri and Greg Wright, economists at LSE and the University of California, firms do cut costs by hiring cheap immigrant labour. But this frees up money to expand production and hire more workers, usually American, to perform complementary, communication-intensive jobs requiring good English. Mexican immigrants actually help keep jobs in America by discouraging firms from "offshoring" in search of lower labour costs. Mr Trump's fiscal accounting is similarly fishy. According to Mr Trump, "taxpayers have been asked to pick up hundreds of billions in healthcare costs, housing costs, education costs, welfare costs" for unauthorised immigrants. He neglects to mention that undocumented residents are already ineligible for most government benefits, but pay a lot in taxes. Studies tend to find that the typical immigrant in America pays more into the system than he or she takes out. The question is a little more complicated when it comes to less-educated, undocumented immigrants. A 2006 study by the Texas State Comptroller found that unauthorised immigrants in 2005 paid $2.09 billion in state and local taxes, but consumed $2.60 billion in government services, mostly in education and health—a fiscal shortfall of $504m. However, the net economic effect of unauthorised workers was reckoned to be strongly positive. Without all those unauthorised workers, the Texas economy would have shrunk by 2.1%, or $17.7 billion, the state's comptroller said. Meanwhile, Mr Trump proposes a boatload of new expenses, such as tripling the number Immigration and Customs Enforcement officers, deporting all "criminal aliens", keeping all apprehended unauthorised immigrants in detention until they can be deported, and mounting major operations to round up and deport undocumented gang members. Then there's also that expensive wall. Mr Trump's ingenious plan for financing all this, when he has one, is to make the Mexicans pay for it. Mr Trump promises to "make America great again", but fails to acknowledge the role Hispanic immigrants play in maintaining America's heft in the global economy. One way immigrants hone America's competitive edge is by helping to keep fertility rates above replacement level. This, in addition to a constant infusion of young new workers from over the border, ensures that America's workforce will continue to expand over the next several decades, even as the number of workers in China, Europe and Japan decline as their populations age. Why throw away this advantage? America’s worker-to-retiree ratios already threaten the long-term fiscal viability of Social Security and Medicare; why make this problem even worse?