Every four years in the United States, a common refrain is heard: “If candidate X wins the White House, I’m moving to Canada.” In 2000, facing the prospect of a President George W. Bush, Eddie Vedder of Pearl Jam memorably vowed, “I’m moving to a different country if little Damien II is elected.” Vedder didn’t keep his word, but Pierre Salinger, former press secretary to John F. Kennedy, did, expatriating himself to France, where he died in 2004.

Most people are more like Vedder than Salinger—quick to make idle threats of relocation but slow to act on them. According to an Ipsos poll conducted in March, 19 percent of Americans would consider moving to Canada if Donald Trump is elected (a slightly smaller number, 15 percent, said they were pondering emigration if Hillary Clinton prevails). The truth is, though, even the most upsetting election result will never be enough to inspire a substantial number of Americans to pull up their stakes and plant them in a foreign land. And despite his gobsmacking success in the Republican primaries, few liberals still take Trump’s policy proposals—or his prospects for winning—seriously enough to be house hunting in Toronto or Winnipeg.

But if there is one thing Trump is dead serious about, it’s mass deportation. If he is elected president, our emigration problem will not involve well-to-do liberals leaving voluntarily, but millions of undocumented Americans being forcibly expelled. Trump has offered an actual plan for dealing with undocumented immigrants—broad in outline, clear in intent. He’s been unwavering on what he intends to do: Deport the approximately 11 million undocumented immigrants in America, construct a wall along the Mexican border, and block remittance payments sent by undocumented immigrants back to Mexico in order to force the Mexican government to pay for that wall. And he has cited a genuinely scary historical precedent. On multiple occasions, Trump has praised President Dwight Eisenhower’s mass deportation effort—although he’s been careful not to mention its name, which was based on a slur used to refer to Mexican migrants who would swim the Rio Grande to cross over into Texas: Operation Wetback.

“Let me just tell you that Dwight Eisenhower—a good president, great president,” Trump said in a November GOP debate. “People liked him. ‘I like Ike.’ ... Moved a million and a half illegal immigrants out of this country, moved them just beyond the border: They came back. Moved them again, beyond the border: They came back. ... Moved them way south. They never came back.”

It won’t surprise any Trump-watcher that he got the details of Operation Wetback wrong. Far from a success on any score, it was a blot on America’s reputation, a program that turned immigration control into a refugee crisis. Operation Wetback is all too well-known to Hispanics, a crucial and cautionary part of their history in the United States. But it’s long been largely, and conveniently, forgotten by the rest of American society. That makes the episode well worth revisiting, given that the leading Republican contender for president is vowing to replicate it—only on a much vaster scale.