When campaigning for the White House, Donald Trump raised concerns about people coming to the United States from parts of the world impacted by terrorism.
He challenged the United States' ability to vet who comes into the country, describing the immigration system as "dysfunctional" and claiming it fails to protect the citizenry.
A Trump administration, he said, would exercise "extreme vetting," especially from war-torn Syria.
"I want extreme. It's going to be so tough, and if somebody comes in that's fine, but they're going to be good. It's extreme," Trump said in Phoenix in August 2016. "And if people don't like it, we've got to have a country folks. Got to have a country. Countries in which immigration will be suspended would include places like Syria and Libya. And we are going to stop the tens of thousands of people coming in from Syria."
WHY HE'S PROMISING IT
In response to terrorism attacks and threats across the world and on U.S. soil, Trump said the United States needs to toughen its admissions process.
Trump called for a "total and complete shutdown" of Muslims coming into the country a few days after a husband and wife — the man, a U.S. citizen born to Pakistani parents, and the woman, an immigrant from Pakistan — killed 14 people and injured 22 others in San Bernardino, Calif., in December 2015.
He reaffirmed this stance after another terrorist attack in an Orlando nightclub in June 2016, when a U.S. citizen born to Afghan parents killed 49 people and wounded more than 50.
"I called for a ban after San Bernardino, and was met with great scorn and anger but now, many are saying I was right to do so — and although the pause is temporary, we must find out what is going on," Trump said on June 13, 2016. "The ban will be lifted when we as a nation are in a position to properly and perfectly screen those people coming into our country."
WHAT NEEDS TO HAPPEN
Trump said he would ask the Homeland Security, Justice and State departments to list "regions and countries from which immigration must be suspended until proven and effective vetting mechanisms can be put in place."
His administration would stop issuing visas to people in places "where adequate screening cannot occur," he said.
Section 212 (f) of the Immigration and Nationality Act allows the president to "suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate," whenever the president finds that their entry "would be detrimental to the interests of the United States."
During the campaign, Trump particularly criticized the arrival of Syrian refugees, but refugees do not get visas to come to the United States. They undergo a different vetting and paperwork process.
Still, Trump as president will have the legal authority to limit refugee admissions.
Section 207 of the Immigration and Nationality Act says the president shall determine the number of refugees who may be admitted per fiscal year. The president is to make such decision before the start of a fiscal year and after consulting the House and Senate judiciary committees.
HOW MUCH WILL IT COST
Trump has not outlined cost estimates for this promise. In a CBS Face the Nation interview in October 2015, Trump said he would offer financial support to create a safe zone in Syria for people afflicted by war, instead of letting them come into the United States.
"I would help them economically, even though we owe $19 trillion," Trump said Oct. 11, 2015, not specifying the extent of that help. "What I won't do is take in 200,000 Syrians who could be ISIS."
WHAT'S STANDING IN HIS WAY
Legally, Trump has the authority to limit and suspend admissions of foreigners into the United States.
"Whether such a broad use of that statutory power would be wise is another question," said Stephen Legomsky, professor emeritus at Washington University School of Law in St. Louis and a former chief counsel at U.S. Citizenship and Immigration Services. "All immigrants to the United States are already checked against an array of intelligence and law enforcement databases. The procedures for screening overseas refugees — the main focus of Mr. Trump's remarks — are especially rigorous and contain additional safeguards in the case of Syrians."
Refugee vetting also already takes one to two years.
"This point is often lost, as some people wrongly point to European terrorism as evidence that refugees pose similar risks in the United States," Legomsky said. "The difference is that the millions of refugees who have arrived in Europe from Africa and the Middle East have traveled by land or by sea without any previous vetting; because of the geographic differences, the refugees whom the U.S. admits from overseas are rigorously vetted before they set foot in the United States."
Provisions under the Immigration and Nationality Act would allow Trump to legally bar the admission of all nationals of Syria or any other country immediately after taking office and without further congressional action, Legomsky said.