Republican presidential nominee Donald Trump speaks in Youngstown, Ohio, on Aug. 15. (Gerald Herbert/Associated Press)

DONALD TRUMP’S proposal to ban Muslims from the country has taken many forms over the past few months. All have been abhorrent. All, including the most recent iteration, would have a consequence that has so far gone ignored: the harm it would do to colleges and universities across the United States.

In his acceptance speech at the Republican convention, Mr. Trump revised his original call for a “total and complete shutdown of Muslims entering the United States” and instead suggested suspending immigration “from any nation that has been compromised by terrorism.” If, in order to qualify as “compromised by terrorism,” a country must have experienced a recent attack, Mr. Trump’s list of undesirables includes citizens of France, Belgium and, well, the United States. Even if Mr. Trump intends to refer to countries the State Department recognizes as nations where terrorist cells operate, allies such as Saudi Arabia are in the mix. In a speech this week, Mr. Trump further refined his proposal as suspending immigration from “some of the most dangerous and volatile regions of the world that have a history of exporting terrorism” while also subjecting would-be visitors to “an ideological screening test.”

Saudi Arabia sent almost 60,000 students to study at U.S. colleges in 2015. India, also on the State Department’s radar, sent almost 133,000. Iran and Turkey sent more than 10,000 each, and Malaysia about 7,000. Because most of these students get the money for their educations from sources outside of the United States, they give a significant funding boost to the schools they choose — and to the U.S. economy. Saudi Arabian students alone contribute $1.7 billion every year, though the number may decrease with the shrinking of the scholarship fund that pays the way for many of them. Indian students contribute $3.6 billion.

Stopping these students from coming to the United States would not only cause economic pain: It would also fly in the face of the cultural exchange that education is supposed to facilitate. Just as U.S. citizens benefit from studying with people of different backgrounds who may have different ideas about the way the world works, students from abroad can take the values they learn here back to their home countries. That is especially important in places such as Saudi Arabia that could benefit most from the democratic ideals U.S. schools try to instill in their students.

Mr. Trump’s “extreme vetting” likely would discourage students from every country from coming to the United States, whether to study or to work, by sending a message that the United States is suspicious of the rest of the world and the people in it. Of course, that has always been a central part of Mr. Trump’s isolationist platform. This is just another reason it is dangerous.

Speaking in Youngstown, Ohio, Aug. 15, GOP presidential nominee Donald Trump vowed to champion immigration reform that would "screen out any who have hostile attitudes toward our country or its principles." (The Washington Post)