Maria Gomez, 22, carries her son David Moises, 1, as the thousands-strong caravan of Central Americans migrants hoping to reach the U.S. border moves onward from Juchitan, Oaxaca state, Mexico, Thursday, Nov. 1, 2018. (AP Photo/Rodrigo Abd)

They were sprinting from the Mexican border straight into oncoming traffic on Interstate 5 in California, zigzagging their way around cars approaching the San Diego port of entry.

“They keep coming,” the narrator said over ominous music. “Two million illegal immigrants in California.”

The footage was from “Border Under Siege,” a 1992 PR film produced by the U.S. Border Patrol. But on the TV screens of millions of Californians, it was a 1994 reelection campaign ad for Gov. Pete Wilson, who had just sued the federal government for failing to stop an “invasion” of undocumented immigrants under the Constitution’s Invasion Clause: Article IV Section 4, which requires the federal government to protect the states against invasion. Wilson was running one of the most anti-immigrant campaigns of his era, seeking to strip all social services from undocumented immigrants under his Proposition 187.

But his militaristic “invasion” metaphor, fueling beliefs that California was literally “under siege," was an old usage.

It’s one of the oldest and most persistent anti-immigration metaphors in the country’s history, employed to oppose Irish Catholics, Asians, Latinos, Germans, Jews and just about everyone except white Protestants of English ancestry who now lives in America. The nation has been perpetually facing a supposed “invasion” from many stripes of immigrants, said Leo R. Chavez, a social sciences professor at the University of California, Irvine and author of “The Latino Threat: Constructing Immigrants, Citizens, and the Nation.”

President Trump’s recent use of the “invasion” metaphor to describe the caravan of thousands of asylum-seeking Central Americans now approaching the southern border is only the latest iteration.

“It’s like an invasion,” he said during his remarks about the caravan Thursday. “They have violently overrun the Mexican border. You saw that two days ago. These are tough people, in many cases. A lot of young men, strong men. And a lot of men that maybe we don’t want in our country.”

The rhetorical tool, Chavez said, “erases the real characteristics of those who wish to come to the United States,” instead creating the image of a single army “bent on destroying our way of life.”

“People have to realize that Trump didn’t invent this rhetoric,” Chavez said. “He’s just able to use it effectively.”

The strategy of framing immigration as an invasion can be traced back to the antebellum era in the 1850s, when the Protestant-majority Know Nothing party, the original “America First” party, rallied against Catholic immigrants. Believing they were controlled by the Pope and therefore incompatible with American liberties, the Know Nothings charged that Catholic immigrants “march and countermarch with the precision of regular soldiers, at the tap of the Popish drum.”

Next, it was the Asians. In an 1889 court decision involving the Chinese Exclusion Act, Supreme Court Chief Justice Stephen J. Field summed up California politicians' attitudes toward Chinese laborers this way: “Their immigration was in numbers approaching the character of an Oriental invasion, and was a menace to our civilization; the discontent from this cause was not confined to any political party, or to any class or nationality, but was well-nigh universal.”

Fear of immigrants was not confined to uneducated working class Americans. “The Immigration Restriction League, founded by young Harvard-educated Boston Brahmins in 1894,” wrote Charles Hirschman in a 2006 study, “advocated a literacy test to slow the tide of immigration. It was thought,” he wrote, “that a literacy test would reduce immigration from southern and eastern Europe, which was sending an 'alarming number of illiterates, paupers, criminals, and madmen who endangered American character and citizenship.”

But for Latino immigrants, such negative attitudes toward their migration didn’t proliferate until the early 1970s, when illegal immigration at the southern border first started rising, as demographers Douglas S. Massey and Karen A. Pren of Princeton University’s Mexican Migration Project found in a 2012 paper examining immigrant metaphors.

Officials under the administration of President Gerald Ford were particularly fond of warning of an “illegal alien invasion," as though America were bracing for a sequel of H.G. Wells’s “War of the Worlds.”

Leonard Chapman, then-commissioner of the Immigration and Naturalization Service, wrote an article in Reader’s Digest in 1976 describing a looming national crisis, titled, “Illegal Aliens: Time to Call a Halt!”

“When I became commissioner in 1973, we were out-manned, under-budgeted, and confronted by a growing, silent invasion of illegal aliens. Despite our best efforts, the problem — critical then — now threatens to become a national disaster,” Chapman wrote.

Then-CIA Director William Colby believed the situation was so pressing that if Mexican immigrants weren’t stopped, they would create a “Spanish-speaking Quebec” in the southwestern United States, according to the book “Operation Gatekeeper: The Rise of the ‘Illegal Alien’ and the Making of the U.S.-Mexico Boundary.”

“The most obvious threat,” Colby said, “is the fact that...there are going to be 120 million Mexicans by the end of the century. . . . [The Border Patrol] will not have enough bullets to stop them.”

Chavez, the UC Irvine professor, said these fears of Mexican immigration, and of nonwhite immigration generally, spread as a result of evolving demographics after changes in immigration law in the mid-1960s. America’s immigration policies in the coming years — and politicians' border rhetoric — was a response to what became known as “the browning of America," he said.

Congress passed the Immigration and Nationality Act in 1965, which replaced what was seen as a racist quota system that, for decades, restricted immigration of Africans, Asians and Eastern Europeans with a system that more equally distributed yearly visas to countries worldwide. But it was the first time countries in the Western Hemisphere and Latin America were subject to any immigration quota. And around the same time, Congress canceled the Bracero program, which allowed temporary migrant workers to come and go across the border for farm labor, making about 450,000 fewer legal visas available to Mexicans per year.

The result, Chavez said, was that while the same number of people from Latin America wanted to come over for work, the vast majority suddenly lacked a readily available legal option. The annual total of people who illegally crossed the border from Mexico increased from fewer than 25,000 in 1958 to more than 450,000 by 1978, according to data from the U.S. Department of Homeland Security.

Chavez said Trump’s rhetoric does not match reality. Trump has often described a crisis at the border, necessitating a wall and troops. But data from the Department of Homeland Security show illegal crossings to be at historic lows, according to data from U.S. Customs and Border Protection.

But the caravan presents a different challenge. Trump has said he may deploy as many as 15,000 members of the military to the border to meet more than 5,000 men, women and children who have been traveling for 21 days from Central America. The president said he plans to take executive action next week seeking to stop “abuse” of the asylum system and to limit the migrants' entry, vowing that they will be confined to “massive tent cities." But he offered few details.

Asked Thursday by reporters if his planned response to the caravan is legal, Trump said, “Oh, this is totally legal. No. This is legal. We are stopping people at the border. This is an invasion, and nobody is even questioning that.”