Editor's note: The following column is excerpted from Tucker Carlson's new book, "Ship of Fools: How a Selfish Ruling Class Is Bringing America to the Brink of Revolution."

The other day I watched a group of young lefties protest the Trump administration’s immigration policies. They were carrying Mexican flags and screaming: "Si, se puede!" Yes we can. 

"Si, se puede" is now the rallying cry of the no-borders left, but it wasn’t always. The slogan first became famous fifty years ago, thanks to Cesar Chavez, founder of the United Farm Workers union. When Chavez said "Si, se puede," he meant something very different: "yes, we can seal the borders."

Cesar Chavez hated immigration. He was Hispanic and left wing, but he called illegal Mexican immigrants "wetbacks," and fought to keep them out of the country. He understood that peasants from Latin America will always work for less than Americans will. That’s why employers prefer them. Immigration undercut his members’ wages and weakened the union. "As long as we have a poor country bordering California," Chavez once explained, "it’s going to be very difficult to win strikes."

In 1969, Chavez led a march down the center of California to protest the hiring of immigrant produce pickers. Marching alongside him was Senator Walter Mondale, and the Rev. Ralph Abernathy, the longtime aide to Martin Luther King. It didn’t seem strange at the time. Liberals still cared about working class wages. 

Years later, Chavez dispatched armed union members into the desert to assault Mexican nationals who were trying to sneak across the border. Chavez’s men beat immigrants with chains and whips made of barbed wire. Illegal aliens who dared to work as scabs had their houses bombed and cars burned. The union paid Mexican officials to keep quiet. Chavez wasn’t embarrassed about any of this. He bragged about it. 

In California, Chavez remains a progressive hero. There’s a state holiday named after him, and at least 25 public schools. Chavez’s life is a reminder of how much the left has changed, and how quickly. For a century, many Democrats agreed with Chavez. They opposed mass immigration because they believed it hurt American workers. As a factual matter, they were right. One study, conducted after the 1980 Mariel boatlift in Miami, found that high school educated Americans saw their wages fall by more than a third after large numbers of Cuban refugees arrived. If you believe in supply and demand, this isn’t surprising. 

Even liberals understood the principle. After the fall of Saigon in1975, Governor Jerry Brown opposed letting Vietnamese refugees into California, on the grounds that the state already had enough poor people. As Brown put it at the time, "There is something a little strange about saying, 'Let's bring in 500,000 more people' when we can't take care of the one million Californians out of work."

Sen. Joe Biden of Delaware agreed; he introduced federal legislation to curb the arrival of the Vietnamese. Even George McGovern, maybe the most liberal Democrat in the Senate, opposed bringing more refugees into the country. "I think the Vietnamese are better off in Vietnam," McGovern said. 

Two decades later, leading Democrats were still wary of mass immigration. As Bill Clinton put it in his 1995 state of the union address, "The jobs they hold might otherwise be held by US citizens or immigrants. The public services they use impose burdens on our taxpayers." No prominent Democrat could say anything like that today without being denounced as racist. Clinton got a standing ovation.

As late as 2006, there were still liberals who cared about the economic effects of immigration. "Immigration reduces the wages of domestic workers who compete with immigrants," explained economist Paul Krugman in the New York Times. "We’ll need to reduce the inflow of low-skill immigrants." That same year, Hillary Clinton voted for a fence on the Mexican border. So did Barack Obama, Chuck Schumer, and 23 other Senate Democrats.

But that was the last gasp of a dying elite consensus. Twenty years after Bill Clinton told Americans they had the right to be upset about illegal immigration, his wife scolded the country for enforcing border controls. The 2016 Democratic platform demanded that all illegal immigrants living in the United States be, "incorporated completely into our society through legal processes." It was now Democratic Party orthodoxy not simply to let illegal aliens stay in the country, but to let them vote. 

What changed? Not the economics of immigration. Supply and demand remained in effect. Predictably, as the country admitted more impoverished immigrants, its own middle class shrunk, becoming a minority of the population in 2015. But Democrats stopped caring. Why? Here’s the short answer, in four simple facts:

One: There are likely more than 22 million illegal aliens within our borders. 

Two: Democrats plan to give them all citizenship. It’s in their platform. 

Three: Studies show the overwhelming majority of first-time immigrant voters vote Democrat. 

Four: The biggest landslide in American presidential history was only 17 million votes. 

Do the math. The payoff for Democrats is obvious: a permanent electoral majority and total control of the country for generations. 

That’s the point, no matter what they tell you. From their perspective, it’s well worth destroying the middle class. 

Excerpted from "Ship of Fools" by Tucker Carlson (Simon & Schuster, October 2018).