Now that he has declared a “national emergency,” all that stands between President Donald Trump and the money he wants to pay for his promised border wall is the American judiciary. And the Constitution. And the attorneys general of California, Nevada, New Mexico and New York. And a vast array of land owners and local governments.

The consequences of free trade are very similar to what happens when a new technology is invented. In both cases goods and services get better and more affordable for everyone, new jobs are created, and some jobs are replaced. So, the next time someone proposes new trade barriers, imagine instead that they had proposed outlawing a new invention.

Nineteenth century historian Thomas Carlyle called economics "the dismal science" because of its predictions about scarcity and poverty. Those are immutable features of all societies, which explains why his snarky term remains widely used. Modern economics writer Thomas Sowell captured the same idea, but expanded upon it. "The first lesson of economics is scarcity: there is never enough of anything to fully satisfy all those who want it," he wrote. "The first lesson of politics is to disregard the first lesson of economics."

Concretely I mean that the bizarre 18th-century idea of liberalism—which is the theory of a society composed entirely of free people, liberi, and no slaves—gave ordinary people the notion that they could have a go. And go they did. In the earliest if hesitatingly liberal societies such as Britain and France, and among the liberi in societies still fully dominated by traditional hierarchies such as Russia and much of Italy, or the slave states of the United States, the turn of the 19th century saw a sharp rise of innovation.