Donald Trump and a pair of Republican senators have come up with a plan to move from catching and deporting illegal aliens to cutting legal immigration to the United States by 50 percent.

The bill they are proposing will keep family members out and welcome instead skilled, educated, well-off immigrants. However, their reasoning is faulty: if, as they claim, their goal is to safeguard American jobs and bid up American wages, this group should be the first to be excluded.

In reality, the ultimate goal of the Trump Administration and these Republicans is to end all immigration – because immigrants are the greatest threat to their efforts to turn America into a third-rate power, a kind of authoritarian Venezuela with nuclear warheads.

Immigrants didn’t just build the United States. First and second-generation Americans made this country great and enlightened; without us, it would never have become a world leader in science and technology and its culture would never have spread around the world the way it did.

Russian dissident writer Vasily Aksenov, the author of a highly prophetic 1979 novel “The Island of Crimea,” immigrated to the United States in the early 1980s. He soon wrote a rather charming non-fiction book titled “In Search of the Melancholy Baby,” detailing the America he dreamed about when he lived in the Soviet Union and the different America he encountered when he finally came here.

It’s a common problem for many newcomers. They have a romantic vision of the United States, formed by watching American movies, listening to its music and reading its books. The reality turns out to be different. Most important, the America they find here somehow fails to live up to its own promise – it seems to them, in some respects, very un-American. Many come to love this reality as well, but their love is almost always preceded by parting with illusions.

Here is what Aksenov writes:

Many immigrants admit that they were utterly shocked by the phenomenon of American boredom. I have already mentioned how alluring the names of American cities sounded to many Russians (as, apparently, they still do to many Europeans as well). Being bored had probably been the least of their concerns – that is if the word “boredom” had occurred to them in this context at all. How could you be bored in a city called Indianapolis or in a state bearing the name of Minnesota, which is sibilant like the wind of adventure? … The American provincialism was one of the things that surprised me most. From afar and from behind the Iron Curtain I had imagined that the States, with its open borders, dozens of languages spoken and global policies, would be the veritable crossroads of universal cosmopolitanism…

Indeed, the “real” American firmament is a remote, isolated, deeply provincial and deadly boring country, uninterested in the outside world and superciliously disdainful of its ways, customs and ideas. It is well-fed, self-contained and perfectly contented. In many ways, it is like Imperial China, the Middle Kingdom. Without waves of emigration washing upon its shores, enriching it with their energies, ambitions and brains and importing new ideas from older continents, it would have been a stagnant backwaters of the world, the way China eventually became and Canada or Australia had been until a couple of decades ago, when they opened up their borders to immigration from different parts of the world.

It could be argued that the American Revolution and its great and lasting achievements – the Declaration of Independence, the Constitution and the Bill of Rights – were the products of the European Enlightenment transported to the New World by immigrants and implemented by the first or second generation of their descendants.

Subsequent great periods of American history coincided with the influx of large numbers of immigrants. This includes industrialization in the second half of the 1800s and, even more to the point, the advent of the American Century – the great efflorescence of American intellectual and artistic life in the middle of the 20th century, achieved mainly by second-generation Eastern European, Irish and Southern European immigrants, as well as Jewish refugees from Nazism.

America is a nation of immigrants; it is in its natural element when immigration flows in freely. Those are always periods of creative ferment and great intellectual, artistic and economic progress.

The current explosion of America’s economic, technological and cultural activity has been fed by the stream of new arrivals, mainly from Asia, Africa, Latin America, Russia and Eastern Europe, that began in the 1980s.

“Real” Americans – white people whose families had been in the United States for many generations – were also involved in large numbers in American achievements, but it was the immigrants who often provided a jolt to the vast country and acted as an impetus for the most talented and energetic. And of course American music owes a huge debt to African Americans, but then again, that portion of US society could hardly be called contented, self-satisfied or prosperous.

On the other hand, periods of low immigration have been associated with blight and stagnation, such as the first half of the 19th century and, more recently, the 1970s, when the proportion of foreign-born Americans dropped to 4.7%, the lowest since 1840.

The nativist backlash is invariably give rise to know-nothing parties and ideas, bringing back the ignorant and intellectually lazy provincialism. It is accompanied by the distrust of science, culture and ideas.

We’re now living through one such period – perhaps the most gruesome and militant wave of xenophobia in American history. Benefiting from a system built in an earlier era, and technologies created by first and second-generation immigrants, the provincial “ugly Americans” are claiming to be anti-government libertarians – a creed promulgated in this country by yet another immigrant, Ayn Rand – but in reality clamoring for authoritarianism – the only form of government they seem to respect.

Nations decay when they build walls around themselves, close up to the outside world and focus inward. It is both the cause of national decay and its symptom. Trump’s America is well on its way toward neo-isolationism. It wants to curb imports, withdraw from international commitment, stop promoting democracy abroad and, as a corollary to these policies, clamp down on immigration. As in Stalin’s Soviet Union, “cosmopolitan” is now an insult in America. Stephen Miller, a White House senior policy advisor, used it to attack a reporter. There is a splendid irony to hear this term, used to attack Jews in the USSR, used by an American Jew.

Of course businesses want visas for skilled workers, universities need foreign students who pay tuition (and professors who teach them), farmers require unskilled labor to gather crops. It has been said that “the business of the United States of America is business”, so Trump and the Republicans in Congress will find it hard to ban immigration entirely. But those nasty immigrants will continue to pollute America with such American notions as tolerance and diversity, and contaminate the country with science and culture.

As such, they will remain a mortal danger to Trump and his nativist supporters.