How the Government Strives to Tell if a Refugee Applicant Is Lying About Being a Christian

— -- President Trump said on Friday that persecuted Christian refugees would receive priority when seeking asylum in the United States, telling the Christian Broadcasting Network in an interview that Christians in Syria have been treated unfairly in the refugee process.

Government workers can likely determine whether those seeking refugee status in the U.S. are lying about their religious affiliations, but falsehoods can still occasionally slip through the vetting process, immigration experts tell ABC News.

"They’ve been horribly treated. Do you know if you were a Christian in Syria, it was impossible, at least very tough, to get into the United States? If you were a Muslim you could come in, but if you were a Christian, it was almost impossible and the reason that was so unfair, everybody was persecuted in all fairness, but they were chopping off the heads of everybody but more so the Christians. And I thought it was very, very unfair. So, we are going to help them," Trump said in a clip of the interview released Friday.

Trump did not give any examples or cite evidence to support his claim that it's more difficult for Christians in Syria to come into the country than Muslims in Syria.

But how can authorities tell whether someone is actually a Christian or not?

A refugee candidate's life is scrutinized during an extensive and thorough vetting process, according to multiple immigration experts.

In the past, refugee applicants were most likely asked about their religious affiliations only if they had applied for resettlement for reasons of religious persecution, said Royce Murray, policy director for the American Immigration Council.

If they had applied citing fear of persecution based on any of the other four categories -- race, nationality, political opinion or membership in a particular social group -- then the topic of religion may have not even been a factor in the interview process, Murray said.

"If it’s a part of the claim, it matters," Murray told ABC News. "If it’s not a part of the claim, it doesn’t matter."

Department of Homeland Security officers who conduct the interviews are highly trained to detect inconsistencies, Murray said. If someone is seeking refugee status for religious persecution -- and is claiming to be a Christian -- the interviewer may ask for evidence supporting his or her claim, Murray said. These can include an affidavit from a church leader, work history and families' statements.

Often, if someone is a Christian minority in his or her country, his or her religion will be stated on the birth certificate, said Denise Gilman, director of the Immigration Clinic at the University of Texas Law School.

For some refugee applicants, providing evidence may prove difficult, because the refugee applicants may have fled under "very urgent conditions" and may not have access to lengthy documentation from every aspect of their lives, Gilman said. But it's up to the DHS officer to verify as much of the information as possible.

DHS officers have to be "very, very attuned to what they're hearing" in order to make a judgment they're comfortable with, said Sam Witten, a 22-year veteran of the State Department and principle deputy assistant secretary of state for refugee programs from 2007 to 2010.

"It puts a burden on the interviewer to get it right -- to know which questions to ask -- to listen," Witten told ABC News.

While DHS officers can ask refugee applicants whatever questions they feel are appropriate, typically, interview questions are heavily security-related, Witten said. Going forward, each DHS interviewer will be tasked "to ask enough questions to figure out -- to their satisfaction -- whether the person meets the requirement that the president is imposing -- that they are a Christian," Witten speculated.

It is not clear if being Christian is the only requirement for the prioritization.

"This is all uncharted territory," said Austin-based immigration lawyer Jason Finkelman. "We’re all trying to figure out what’s going on."

The vetting process is already so "extreme," that Finkelman said he doesn't know how much more extreme it can get.

Witten echoed that sentiment, saying that DHS and the State Department are already so "thorough" and "careful," calling the vetting process in place already "very extensive."

"No one wants a refugee to come into the country who would threaten national security," he said.

Trump's intention to prioritize persecuted Christians in the refugee process could entice many to lie about their religious affiliation, Witten said, and Gilman said she wouldn't be surprised if religious affiliation becomes a staple in the screening process going forward.

It is possible, but not likely, for the occasional falsehood to slip through, Gilman said.

"In general, those of us who work in the refugee process believe the vetting is so intensive and lengthy and extreme that there is unlikely to be a significant level of fraud," Gilman said.

But still, it may be hard to prove whether someone is truly Christian, Finkelman said, adding that in the future, a religious test may be necessary to accomplish that.

"If confronted by someone who is a really good liar, they could fool anybody," said Benjamin Johnson, executive director of the American Immigration Lawyers Association. "There’s no guarantees."

In an interview on Sunday on ABC News' "This Week," White House press secretary Sean Spicer said appropriate vetting will be put in place to ensure that refugees are seeking asylum in the U.S. for "peaceful purposes."

When asked if this vetting process would include a religious test, Spicer said "no."

"What we're going to do is make sure that people who have been persecuted for either religious or other reasons have an opportunity to apply and go through a vetting system that ensures they're coming to this country to seek asylum, to seek a new life for themselves or their family, but to do so with peaceful purposes," he said.

In 2016, 15,302 people who arrived in the U.S. from Syria identified as Muslim, while 93 people who arrived from Syria identified as either Catholic, Christian, Protestant or Jehovah's Witness, according to the Refugee Processing Center, an agency overseen by the U.S. State Department.

During his campaign, Trump promised to cut down or stop the number of refugees entering the U.S. An executive order signed by the president last week stipulates how the refugee program will be reinstated in 120 days.

The executive order states that the refugee program will be suspended for 120 days, after which it will be resumed "only for nationals of countries for which the Secretary of State, the Secretary of Homeland Security, and the Director of National Intelligence have jointly determined that such additional procedures are adequate to ensure the security and welfare of the United States."

Trump's executive order is a "fundamental violation of the constitution," Johnson said. "As a matter of law, I'm not even sure that we can say that we can prioritize one form of religious persecution over another."

Gilman expressed concern over Trump's intention to prioritize Christian refugees because the program is "set up to give protection to those in gravest need."

"The refugee and asylum programs are to protect the most vulnerable people on the planet from near or certain death," Finkelman said.

Trump defended the executive order in a statement Sunday, saying that while "America is a proud nation of immigrants," it will continue to show compassion to those fleeing oppression "while protecting our own citizens and borders."