WASHINGTON, D.C. --President Donald Trump says his halt to immigration from seven Muslim-majority nations and ban on refugees is being done in the name of national security. But it's not clear whether these measures will help prevent attacks on American soil, and they could embolden extremists who already view the U.S. as at war with Islam.
The admissions ban announced Friday also does not directly address a more urgent law enforcement concern: homegrown violent extremists already in the United States who plot their attacks without any overseas connections or contacts.
"The primary terrorism-related threat facing the U.S. today comes from individuals living here who become inspired by what they see on the internet who carry out attacks independent of any terrorist organization," said John Cohen, a former Department of Homeland Security counterterrorism official who worked in government under Democratic and Republican administrations and who has been involved in refugee vetting policy.
The FBI has for years been concerned by the prospect of airplane bomb plots and terrorists dispatched from overseas to commit violence in America. But the ascendancy of the Islamic State, and the group's ability through slick and easily accessible propaganda to reach followers in all corners of the country, has been a more immediate challenge - and a more realistic danger - for Western counterterrorism officials.
The executive order suspends refugee admissions for 120 days and bars all immigration for 90 days from Muslim-majority countries with terrorism concerns: Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen. It indefinitely bars the processing of refugees from Syria, a country that's been of particular alarm to the FBI even though the number of Americans who have looked to travel there to fight with the Islamic State has been dwindling.
PHOTOS: Demonstrators protest Pres. Trump's immigration policy
Even so, the list omits Saudi Arabia, where the majority of the Sept. 11 hijackers were from, and some of the most high-profile recent attacks of violence involved attackers who were born in the U.S. or whose families weren't from any of the seven nations singled out.
Omar Mateen, the man responsible for the Orlando nightclub shooting, the deadliest terror attack in the U.S. since the Sept. 11 attacks, was born in New York to Afghan parents. Syed Rizwan Farook, who took part in the December 2015 San Bernardino attack, was born in Chicago. His wife, Tashfeen Malik, had been living in Pakistan and visiting family in Saudi Arabia before she passed the background check and entered the U.S.
The brothers who bombed the Boston Marathon were ethnic Chechens who had been lived in the U.S.
In general, Islamic extremists have accounted for a minuscule amount of the roughly 240,000 homicides since Sept. 11, 2001, and people with ancestry from the seven nations in the executive order are responsible for a small fraction of arrests and disrupted plots, said Charles Kurzman, a sociology professor at the University of North Carolina at Chapel Hill who has studied the issue.
SEE ALSO: Iraqi detained at JFK was coming to Houston
"I can only conclude that this is whipping up fear and hostility toward Americans who have family background from these countries," Kurzman said.
Still, while refugees are subject to extensive screening - including in-person interviews, checks with law enforcement databases and collection of biometric data - the process is not perfect. FBI counterterrorism officials have long expressed concern about the lack of background information on refugees from Syria, a home base of the Islamic State, and Director James Comey has said that he could not guarantee a mistake-free vetting process.
There have been isolated incidents of refugees later accused in terror-related plots.
An Iraqi refugee who entered the U.S. in 2009, for instance, pleaded guilty in Houston in October to attempting to provide material support to the Islamic State. Two Iraqi refugees who lived in Kentucky are now in prison after having been convicted in a plot to send sniper rifles, Stinger missiles and money to al-Qaida operatives waging an insurgency back home.
The man accused in the November car-and-knife attack at Ohio State University was a refugee originally from Somalia who, as an adolescent, moved with his family to the United States in 2014 after living in Pakistan.
Though not immune from lapses, the screening process has improved over the years and refugees remain "heavily scrutinized," their backgrounds and personal information checked against multiple data sets, Cohen said.
He said he was concerned that the refugee ban could deter Muslim-majority countries from cooperating with the U.S. on policy matters and could embolden an extremist already bent on violence.
"That's something," Cohen said, "that law enforcement folks are going to be factoring into their violence prevention efforts."