Donald Trump’s latest provocation — calling for “a total and complete shutdown of Muslims entering the United States until our country’s representatives can figure out what is going on” — has earned him scathing rebukes from public figures around the world, including many of his fellow Republican presidential candidates. A poll from NBC News and the Wall Street Journal indicates that only a quarter of Americans agree with his proposal, while 57 percent oppose it. However, in a separate poll, conducted by the Associated Press and GfK just prior to Trump’s “shutdown” statement, “54 percent of Americans, including about three-quarters of Republicans, about half of independents and over a third of Democrats, said the United States takes in too many immigrants from the Middle East.” In other words, even many of those who reject the Trump position believe we should reduce immigration from Muslim countries.

As Mark Krikorian of the Center for Immigration Studies wrote last week, “Trump is playing the part of your crotchety Uncle George holding forth on politics at the Thanksgiving dinner table. But the reason his careless and sloppy immigration commentary resonates is that no one else in public life is willing to address issues that worry — and, at this point, frighten — people. If ‘respectable’ politicians refuse to even talk about the real problems caused by mass Muslim immigration, then a larger and larger share of the public will turn to carnival barkers unafraid of elite disapproval.”

The question we should be discussing is whether current levels of immigration — both Muslim and non-Muslim immigration — are compatible with genuine cultural assimilation, broad-based economic prosperity, and U.S. national-security interests. According to a Pew Research Center survey conducted in March and April, a large plurality of Americans (49 percent) — including an equally large plurality (49 percent) of independents, 67 percent of Republicans, and 33 percent of Democrats — think overall immigration levels should be reduced. Yet their viewpoint has relatively few champions among our political elites.

Needless to say, Krikorian is correct that the gap between elite and popular opinion on immigration helps explain the Trump phenomenon. Here’s David Frum, writing in the Atlantic:

“Even as immigration becomes ever-more controversial with the larger American public, within the policy elite it preserves an unquestioned status as something utterly beyond discussion. To suggest anything otherwise is to suggest — not merely something offensive or objectionable — but something self-evidently impossible, like adopting cowrie shells as currency or Donald Trump running for president.

“Only Donald Trump is running for president — and doing pretty well, too. He’s led polls of Republican presidential candidates for now nearly 5 consecutive months. Pundits (including me!) who had insisted that it was impossible that he could actually win the nomination are now beginning to ponder what will happen if he somehow does. And while it’s clear that the immigration issue does not constitute all of Trump’s appeal, it’s equally clear that the issue has been indispensable to that appeal.”

The main lesson of Trump’s rise is the same lesson we have learned from countries throughout Western Europe. Simply put: When a nation’s political establishment either ignores or downplays legitimate, widespread public concerns, anti-establishment figures (of varying degrees of respectability) will fill the void.