A fanatic has been defined as someone who can't change his mind and won't change the subject. It's a good description of Donald Trump, who began his quest for the presidency stoking fear of foreigners and used this year's final debate to keep doing it, as he has throughout his presidency.

Foreigners who come to America — with or without authorization — are viewed with hostility by this administration. It has diverted military funding to build Trump's border wall. It has separated thousands of foreign children from parents who came without permission — and then failed to reunite hundreds of these families. It has cut refugee admissions by some 90% and legal immigration by half. It has declared war on "sanctuary cities."

From the beginning, he's combined pitiless policies with venomous rhetoric. In announcing his candidacy in 2015, he said of Mexicans coming to the U.S.: "They're bringing drugs. They're bringing crime. They're rapists."

In the debate, Trump again invoked that scary specter. Under previous administrations, he claimed, "A murderer would come in, a rapist would come in, a very bad person would come in - we would take their name, we have to release them into our country."

His own Department of Homeland Security begs to differ. In 2018, it said that past enforcement practices were "highly efficient at repatriating Mexicans, convicted criminals, and single adults who do not seek humanitarian relief" — including 97% of those with criminal records.

Another Trump obsession is sanctuary cities, which limit police cooperation with U.S. Immigration and Customs Enforcement. He has threatened to cut off federal funds to such jurisdictions. In October, ICE launched raids in several of these places, netting 170 arrests. Trump even wanted to deny coronavirus relief money to states that have sanctuary cities.

It was a 2015 incident in San Francisco that candidate Trump exploited in his demonization of these policies: A woman was killed by a bullet fired by an undocumented Mexican felon who had been released from jail, though a jury ruled the shooting an accident.

He would have us believe that sanctuary cities give a free pass to undocumented criminals, exposing residents to rampant villainy. But sanctuary cities don't treat foreigners who commit crimes any better than U.S. citizens. They merely refuse to serve as immigration agents for the federal government by holding arrestees after they are entitled to be released.

In that, they are respecting constitutional guarantees. In 2018, a federal court ruled that the Los Angeles Sheriff's Department's practice of assisting ICE by "detaining individuals beyond their date for release violated the individuals' Fourth Amendment rights."

Nor is there any reason to believe sanctuary policies present a danger. A new study by Stanford political scientist David K. Hausman concludes that "sanctuary policies reduce deportations by one-third, but that those policies do not reduce deportations of people with violent criminal convictions" and have "no measurable effect on crime."

His study echoes the findings of previous research. True, there are the occasional cases of undocumented foreigners who commit lurid crimes after being released from custody. But it's not the American way to lock up a large number of peaceable folks to incapacitate a small number of dangerous ones.

The dangerous ones are indeed small in number. In fact, their law-abiding habits put the rest of us to shame. Cato Institute researcher Alex Nowrasteh analyzed the voluminous data from Texas and determined that "illegal immigrant conviction rates are about half those of native-born Americans."

Trump and his supporters claim they don't object to legal immigrants, only the other kind. But his administration has choked off entry to foreigners coming here through approved channels. Among the methods: blocking travel from several Muslim-majority countries, imposing wealth tests, slowing down the processing of applications for permanent residency status and barring new skilled-worker visas for a wide variety of jobs.

But if Trump is having his way on immigration and satisfying the MAGA crowd, he's losing the public. "Thirty-four percent of Americans, up from 27% a year ago, would prefer to see immigration to the U.S. increased," Gallup reported in July. "This is the highest support for expanding immigration Gallup has found in its trend since 1965."

Those who want to curtail immigration can revel in Trump's efforts to seal off America from the flow of foreign arrivals that have enriched our economy and society from the beginning. But come Election Day, they may find he's given their cause the kiss of death.

Steve Chapman blogs at http://www.chicagotribune.com/news/opinion/chapman. Follow him on Twitter @SteveChapman13 or at https://www.facebook.com/stevechapman13. To find out more about Steve Chapman and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.