I was packing up 37 years’ worth of books and materials the other day when I found two packets of beautifully embossed bookmarks from a Chinese student. I remembered him. He sat in the front row of my “Introduction to Russian History” course, and he never missed a beat.  He showed up for every office hour, read all the material, asked questions after class and earned an A.

I remembered the rest of the Chinese students, too, although not individually. There were 15 or so of them in a class of 120. They sat in the back row huddled together. When exam time came, they all flunked. Reading their exams, I understood why they had not come to see me when I reached out to them. They didn’t know enough English to ask the questions they needed answers to. One of my T.A.s spoke Mandarin. Even that didn’t help.

Over the past five years, Chinese students have flooded American campuses. Currently, 974,926 international students are studying in the United States; about a third of them are from China. These visitors have not always gotten good press. About 8,000 Chinese students were expelled from U.S. colleges and universities in 2013-14, primarily because of cheating or failing. Chinese applicants have been accused of cheating on the TOEFL (a mandatory English-language proficiency test international students must take to gain admittance into a U.S university). Articles suggesting many are not prepared for the rigors of higher education in the United States abound.

I feel for them. I remember studying in the Soviet Union in the 1970s, trying to understand lectures in Russian on study abroad. But I had basic language skills. A lot of the students I encounter today do not. Last year, one of my Chinese students could barely even form the letters of the Roman alphabet. As a professor, I’m not always sure what to do. I don’t water down my lectures, but I present the material in as many different mediums as I possibly can, hoping that one medium might be more comprehensible than the next. Still in these large courses that are already a teaching challenge with increasing student enrollments, I know that I’ll lose most of my Chinese students.

Despite these obstacles, though, I would never suggest that these students shouldn’t come. From a purely economic point of view, they bolster our economy. In 2014, these students contributed more than $30 billion to the American economy, according to a report issued by the U.S. Department of Commerce. International students, often paying full freight, also help colleges address budget shortfalls (especially as state governments cut funding). At my university, there is a huge incentive to accept international students because they pay the same tuition, $35,000 per year, as out-of-state students as opposed to the $12,000 a year in-state students pay.

But at the end of the day, it’s not really about the money. We need these international students here for reasons that go way beyond dollar figures. Whether from China, India, the Middle East or Africa, they help counter what I call the new isolationism. Today, we’re dealing with dangerous Islamophobia; one of our presidential candidates is suggesting that we ban all Muslims from entering the country. For many, the answer to immigration is simply to build a higher wall between the United States and Mexico. Foreign students can help counter the fear and ignorance that fuel these policy positions. Their presence, and their relationship with Americans, helps shape, inform and correct how we perceive the rest of the world.

This is all the more important because few Americans have opportunities to travel outside the country. In 2015, when a record 974,926 foreign students were pouring into American colleges and universities, just 304,467 American students studied abroad. By the time they graduate, fewer than 10 percent of American undergraduates will have studied abroad. Of the students who have that opportunity, more than 50 percent visit the United Kingdom or Europe. That means there are large swaths of the world that students have very little experience with.

It’s not just that our students aren’t curious about Asia, Africa and the Middle East. There are a million factors keeping us at home. The security situation in countries such as Syria, Iraq and Yemen is such that students who want to study Arabic are limited these days to Morocco, Jordan, Oman, and the United Arab Emirates.

Increasingly, universities, my own included, have International Travel Safety Oversight Committees that judge the relative safety of students and faculty traveling abroad based on their own reviews and the State Department’s travel warnings. Universities are legally and financially responsible for students and faculty members who travel under their auspices and are acutely conscious of insurance and liability issues. Fractured relations between countries keep students at home as well. Right now, the United States sends no undergraduate students to Pakistan, despite the fact that the Fulbright program sends more Pakistani students to the United States each year than any other country. Iran is another problem; U.S.-imposed sanctions have kept American students out of the country, although private institutes and foundations are doing what they can to correct this.

This matters now, more than ever. Donald Trump is selling the United States as an isolationist country, one that would bomb Iran and put a wall up in Mexico. We can do a lot to counteract Trump’s vision of the world. Internationalizing our campuses strengthens our ability to reach out to those who come here. It helps us become more curious about the rest of the world and about the lives and cultures of the people who are landing on our shores.

But we need to be careful.

Internationalizing our campuses is about more than numbers. It is about our willingness to reach out to these foreign students once they are here. Otherwise, they become  ghettoized.”  Our universities need to encourage American students to spend more time with our international visitors. Right now, that’s not often the case.  A student of mine from Pakistan is currently studying in a college in the Midwest. She tells me that the friends she has made have all been other foreign students. Americans, she says, don’t really reach out. All of them, she said, walked around wearing headphones or  earbuds. A colleague who spent three and a half years in Iraq tells me that when she returned, no one really asked her about the experience aside from what language was spoken there and what the food was like. I suspect that what she encountered was all too familiar to many people reading this article.

So I say to those students from other countries, come. As you move around the culture, the English will also come. As you buy your groceries, watch TV, and begin talking to American students, at some point all those words being uttered by those of us at the front of the lecture hall will congeal into sense. But the onus is not only on the students who come from abroad.We don’t have to travel to be international. What we need is a deep curiosity about how the rest of the world lives, a curiosity that, I fear, is at present lacking. Once we truly internationalize our vision, the world that Trump wants to build wouldn’t have a chance.