Protesters assemble at John F. Kennedy International Airport in New York, Saturday, Jan. 28, 2017 after two Iraqi refugees were detained while trying to enter the country. On Friday, Jan. 27, President Donald Trump signed an executive order suspending all immigration from countries with terrorism concerns for 90 days. Countries included in the ban are Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen, which are all Muslim-majority nations. (AP Photo/Craig Ruttle)
Protesters assemble at John F. Kennedy International Airport in New York, Saturday, Jan. 28, 2017 after two Iraqi refugees were detained while trying to enter the country. On Friday, Jan. 27, President Donald Trump signed an executive order suspending all immigration from countries with terrorism concerns for 90 days. Countries included in the ban are Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen, which are all Muslim-majority nations. (AP Photo/Craig Ruttle) Credit: Craig Ruttle

Washington — 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 that the measures will help prevent attacks on American soil, and they could wind up emboldening extremists who already view the U.S. as at war with Islam.

Recent high-profile acts of deadly extremist violence have been carried out either by U.S. citizens or by individuals whose families weren’t from the nations singled out. And the list of countries doesn’t include Saudi Arabia, where most of the Sept. 11 hijackers were from, or other places with a more direct link to terrorism in America.

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 under Democratic and Republican administrations and who has been involved in refugee vetting policy. “Dealing with that threat should be a top priority for this administration,” Cohen said.

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 concern to the FBI even though the number of Americans who have looked to travel there to fight with the Islamic State has been dwindling. But the culprits of recent terror attacks aren’t linked to the countries singled out by Trump’s order.

Omar Mateen, the man responsible for the Orlando nightclub shooting, the deadliest terror attack in the U.S. since Sept. 11, 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 living in the U.S.

While refugees are subject to screening — including in-person interviews, checks with law enforcement databases and collection of biometric data, when available — the process is not perfect.

FBI counterterrorism officials have long expressed concern about the lack of background information about 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. And 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, Cohen said. He said he was concerned that the refugee ban could deter Muslim-majority countries from cooperating with the U.S.