The GOP's nativist summer: how the Republican Party lost its marbles over immigration.

• Author: Welch, Matt

WHEN DONALD TRUMP first theatrically escalatored down the Trump Tower foyer and into our political lives on June 16, few commentators were predicting that the billionaire reality TV star would spend his summer dominating the Republican 2016 field, let alone driving a sustained debate over one of America's most intractable policy challenges.

No, they were too busy laughing. The Washington Post's Philip Bump headlined his reaction, "Donald Trump's spectacular, unending, utterly baffling, often-wrong campaign launch." National Review's Kevin D. Williamson was even more withering: "Witless Ape Rides Escalator."

Attracting special scorn was the real estate developer's incoherent 123-word rant about Mexicans: "When do we beat Mexico at the border? They're laughing at us, at our stupidity. And now they are beating us economically. They are not our friend, believe me. But they're killing us economically. The U.S. has become a dumping ground for everybody else's problems. ...When Mexico sends its people, they're not sending their best. They're not sending you. They're not sending you. They're sending people that have lots of problems, and they're bringing those problems with us. They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people. But I speak to border guards and they tell us what we're getting. And it only makes common sense. It only makes common sense. They're sending us not the right people."

It was almost too gross to fact check. No, Mexico is not "beating," let alone "killing," the U.S. economically--the comparative per-capita GDP ratio is still 5-to-I in favor of the yankees. (Also, international economics is not a zero-sum competition.) Immigrants from Mexico are not disproportionately more criminal than the native population--in fact, native-born American men between 18 and 39 are twice as likely as immigrants from that cohort to be incarcerated, a ratio that has been stable for decades. Additionally, Mexico isn't "sending" its citizens northward in any organized sense, though that didn't stop Trump from claiming in the ensuing weeks that the Mexican government is engaged in a Mariel-boatlift-style prisoner-exporting operation to the U.S., only "more sophisticated" than Fidel Castro's. Even his relevant policy proposals--taxing auto parts made in Mexico, forcing the government there to pay for a 2,000-mile border wall--would involve, respectively, violating a longstanding free-trade agreement...