Every Monday, I walk into a clinic examination room eager to welcome a refugee new arrival to the United States. I smile broadly and ask how they are adjusting to Minnesota, often joking about the weather or warning about the dangers of frostbite. We talk of their journey to America, often a years-long, harrowing story of loss and resilience. Of what it feels like to have a roof over your head, enough food to eat, and new challenges of learning English, putting the kids in school and getting a job. The feeling is one of relief, and hope, and no small measure of anxiety about the road ahead. I remind them of the strength, courage and optimism that got them to the U.S., urging them to call on those skills in the days ahead. I have been delivering this same message since I was a third-year medical student in 1979, responding to the Southeast Asian refugee crisis, along with many other Minnesotans.

I do this work in refugee health knowing that in fact refugees are perhaps the most "extremely vetted" group to enter the U.S. every year — both from a medical and a security standpoint. From a medical perspective, they are the most carefully screened; more screened than you or I after travel to exotic locations, or tourists and business travelers coming to America. The Centers for Disease Control and Prevention's Division of Global Migration and Quarantine, in collaboration with the International Organization for Migration, runs a huge international program of screening and treatment of refugees for tuberculosis, intestinal parasites, malaria and vaccine-preventable diseases. I joke that my life as a tropical medicine specialist in the U.S. has become a bit more mundane because of their outstanding work, saving lives, saving money and protecting the public health.

Of all the people entering the U.S., refugees are also the most heavily vetted from a security perspective, including multiple interviews by the departments of Homeland Security and Defense. Refugees are asked to tell their story over and over to identify any inconsistencies. Hundreds of experts are involved along the way, helping people who have been through hell — children and women who are victims of sexual assault, those who have been tortured, or perhaps helped the U.S. as interpreters during war. Remember the definition of a refugee — they had to flee across an international border, fearing persecution — they did not choose to flee. Less than 1 percent of the world's refugees make it through to a country of resettlement. For the U.S., that has meant less than 100,000 refugee arrivals every year.

As a scientist and physician, I think about the evidence basis for decisions by the Trump administration and can only conclude that the president has not done his homework on our vetting processes for refugees. His decision last week to temporarily halt the refugee resettlement program has not been made based on scientific evidence. The xenophobic, nationalist message he sends with such decisions generates fear and worsens our relationships around the world.

When I speak to audiences about refugee and immigrant health, I like to ask people to stand up if they are a first-generation immigrant or a descendant of immigrants to America. In a U.S. audience, 99.3 percent of people should stand up. Often they hesitate, forgetting their own immigrant roots.

My grandfather came from Sweden at age 8, speaking no English, and became a very successful physician. Two generations later, I can only say "thank you" in Swedish.

Perhaps what disturbs me the most about this suspension on legal immigration is the message it sends about our core values as Americans, being true to our core identity as a nation of immigrants. "Give me your tired, your poor, your huddled masses yearning to be free" is exactly what the U.S. Refugee Program has been doing for decades, and it is at risk.

In 1938, President Franklin Roosevelt was criticized for his lack of response to the plight of European Jews. He responded by convening a conference in Evian, France. Thirty-two countries attended, yet only Costa Rica and the Dominican Republic agreed to increase their refugee quotas. Hitler and the Nazis used this as a propaganda tool.

Decades later, another crisis prompted another international conference. This time it was again the United States, in Lake Geneva, near Evian, on the plight of the hundreds of thousands fleeing the Communist victory in Vietnam, Laos and Cambodia. Vice President Walter Mondale was the keynote speaker, and in an emotional call to action he compared the gathering to the 1938 Evian Conference, which he said "failed the test of history." He pleaded with the delegates to join the U.S. in rescuing what were known as the "boat people." He said: "History will not forgive us if we fail. History will not forget us if we succeed." The U.S. Refugee Act of 1980 was passed, and more than 3.5 million refugees have entered the U.S. since that time.

Human migration will always occur, fleeing from war or choosing to move for a better life. Right now the numbers of displaced are as high as after World War II — 65 million worldwide, and 21 million refugees; half of those are children. More than a billion of us meet the U.N. definition of a migrant — a person who is living outside his or her country of origin for more than one year. And 1.2 billion tourists traveled the world in 2015. Singling out refugees and halting their flow is an example of foreign policy gone horribly wrong. The U.S. refugee resettlement program is a model for "extreme vetting" of a migrant group; it should be singled out as a role model of a program that is a humanitarian, public health and security success.

In the meantime, I will keep going to clinic every week, working with my Somali, Hmong, Bhutanese Nepali, Cambodian, Vietnamese, Russian and other refugee and immigrant colleagues from around the world. They teach me so much about strength and resiliency. They are nurses, doctors, pharmacists, social workers who, because they came dreaming of a better life, make me a smarter, kinder and better person, and America a better country.

Dr. Patricia Walker is a professor of medicine at the University of Minnesota and a staff physician at HealthPartners Center for International Health in St. Paul. She is president of the American Society of Tropical Medicine and Hygiene.