President Donald Trump's order to crack down on visa overstays will target mostly African and Asian nations.

And the effort will deal with only about 12% of foreigners who legally enter the U.S. on short-term visas but remain in the country after that visa has expired.

Trump on Monday ordered the secretaries of State and Homeland Security to develop plans to crack down on countries whose citizens are most likely to overstay their visas, a long-term problem that is now the biggest driver of illegal immigration into the United States. In 2018, more than 569,000 foreigners overstayed their visas, according to Homeland Security data.

In an effort to slow that trend, Trump ordered Secretary of State Mike Pompeo and Acting Homeland Security Secretary Kevin McAleenan to implement a broad series of punishments for countries whose citizens overstay their tourist and business visas more than 10% of the time.

More:President Donald Trump orders crackdown on 'visa overstays'

Those punishments can include limiting the number of people who can travel to the U.S. from any one country, requiring foreign travelers to post "admission bonds" that would be repaid once they leave the country and requesting more documents from foreigners seeking visas.

Here's a look at the countries that could be targeted by the president's order:

21 countries, mostly in Africa and Asia

Under the guidelines set out by Trump on Monday, 21 countries could face sanctions because 35,442 of their citizens overstayed their U.S. visas in 2018, according to Homeland Security data.

The region facing the most potential impact is Africa, home to 13 countries on the list ranging from Angola to Chad to Sudan. The biggest target by far is Nigeria, which saw 29,004 of its citizens overstay their visas in 2018.

Another six countries on the list are located in Asia, and several have been embroiled in bloody armed conflicts, such as Afghanistan, Syria and Yemen.

Rounding out the list are the island nations of Palau and the Federated States of Micronesia, who combined for 13 total visa overstays in 2018.

Trump method punishes small countries

The president could have chosen to punish countries where the largest numbers of total visa overstays came from.

For example, more than 34,000 Brazilians, 15,000 Chinese, 10,000 Indians and 10,000 French overstayed their visas in 2018.

But Trump chose to target countries where the overstay rate — not the total number of people who overstayed their visas — was high. That means Brazil, China, India and France will not be affected by Trump's order since their citizens' combined overstay rate was 0.9%.

But smaller countries like Bhutan, a mountainous nation squeezed between China and India, could face sanctions since 46 of 398 of its people who traveled to the U.S. in 2018 overstayed their visas, a rate of 13.1%.

Critics say its no coincidence that the Trump administration chose a method that punishes mostly African and Asian countries and spares European countries and other U.S. allies.

"This is Stephen Miller's way of operationalizing his immigration strategy to 'make America White again' by covering his tracks with data to disguise the underlying White nationalist objectives of the policy," said Douglas Rivlin, director of communications for America’s Voice, an immigration advocacy group, said of the president's immigration adviser.

Foreign students not targeted

Trump made clear that he would focus his order on foreigners traveling on a B1 visa used by business travelers or a B2 visa used by tourists.

But Homeland Security data show that foreigners traveling on student visas, research visas, and cultural exchange visas are more likely to overstay their visas.

In 2018, of the 1,840,482 foreigners who entered the country on those visas, 2.1% stayed past their expiration date. In the same year, of the 15,257,468 foreigners who entered the country on business or tourist visas, 1.9% overstayed.

Here's the full list of countries whose citizens overstay their U.S. tourist and business visas more than 10% of the time in 2018: Afghanistan, Angola, Bhutan, Burundi, Cabo Verde, Chad, Republic of the Congo, Djibouti, Eritrea, Georgia, Laos, Liberia, Mauritania, Federated States of Micronesia, Niegria, Palau, Somalia, South Sudan, Sudan, Syria and Yemen.

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