Reports that one of the terrorists that struck Paris last week might have entered the country through the unofficial refugee stream through Greece has greatly amplified political questions about the extent to which the United States welcomes refugees or asylum-seekers from that region.

Governors of multiple states, acting from an abundance of caution (and probably a not-insignificant amount of politics), have told the federal government that they will refuse any refugees from Iraq or Syria. Several candidates for the Republican presidential nomination, including Ted Cruz and Jeb Bush, have suggested a religious test for admission.

At its heart, the question is one of safety. Can the United States ensure that those we welcome will not conduct acts of violence once they arrive? To which there's a simple answer: No, no more than we can prevent citizens of the United States from conducting acts of violence. (Worth noting: Several of the identified terrorists in Paris were French or European.)

So the question becomes more nuanced: How do we balance a desire to protect people from a dangerous area with the desire, as much as we can, to protect ourselves? And are the strategies above effective?

The United States has welcomed asylum-seekers and refugees throughout most of its history, of course, and so there already exists a process through which applicants must go. (In 2013, the United States admitted nearly 70,000 refugees.) The difference between seeking asylum and refuge is where the request originates. Those already in the United States apply for asylum. Those overseas apply as refugees. Since most of those affected by the violence in Iraq and Syria haven't been able to make it to the U.S. -- the Atlantic Ocean providing a much bigger obstacle than the Mediterranean -- the debate has largely focused on those seeking refugee status.

The process, called the United States Refugee Admissions Program, or USRAP, is run by the U.S. Citizenship and Immigration Services branch of the Department of Homeland Security. (Neither USCIS or DHS would comment on the record for this article.) Under the USRAP, refugees are given one of three priority levels determining how expediently their cases are handled -- after which, the screening begins.

Refugee applicants receive more screening than any other traveler entering the United States, according to DHS. Biometric information (like fingerprints) and biographic data (relationships, family members, personal history) are checked against a number of federal and international databases, including ones maintained by the State Department, the FBI and the intelligence community. Until those checks are completed and passed, refugees cannot enter the country.

David Leopold, an immigration attorney from Cleveland and former president of the American Immigration Lawyers Association, has assisted scores of asylum-seekers through the same screening process.

"If things pop up or if there's any kind of security hit, those applications are not approved. They're investigated -- and that can take days, it can take months, it can take years," Leopold said. He's had clients that applied for asylum and who received an "administrative processing hold" -- the official term for a security hold. Those cases have taken months to get resolved, without the applicants (or their attorneys) knowing why the status has been delayed.

What's more, he said, Arabic names offer a whole other level of complexity. Arabic names often derive from the names of fathers and grandfathers, meaning that there are a lot of similar names. "I've seen situations where professionals have been vetted -- not just by security but because they've published, they've made names for themselves -- have been caught in a security hold," he said. "Situations where people are clearly eligible to come into the United States have been held back for months or months because the FBI is doing background checks."

One of the concerns raised by critics of the plan to allow Syrian refugees is that the FBI might lack records on potential threats. This was admitted in House testimony by FBI director James Comey, who noted that our extensive efforts in Iraq have made that country's security database more robust. Leopold agreed that this was a problem, but notes that a lack of a red flag could also mean that the applicant was not involved in any suspicious activity. He also noted that the background screening process includes the relationships of the applicant, increasing the odds that a suspicious link would be uncovered.

So what can a concerned governor do?

Florida Gov. Rick Scott (R) wrote in a letter to House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell that his understanding was that his state "does not have the authority to prevent the federal government from funding the relocation of these Syrian refugees to Florida" -- an opinion that's apparently at odds with the Republican governors of other states.

But it appears that Scott is correct. Sources at several refugee agencies confirmed to The Post that states lack authority, as did Leopold. "The governor has no right to block anyone from coming," he said. "Resettlement is determined by the Department of State, and immigration is a completely federal matter." (In 2012, the Supreme Court reaffirmed federal jurisdiction over immigration.) Since state governments usually act as pass-throughs for federal relief money that ends up going to refugee programs, Leopold said, it's possible states could exert some leverage there -- but it's tricky. Blocking only support for Syrians, for example, could result in charges of discrimination.

On Monday, the chairman of the House Homeland Security Committee asked President Obama to suspend the admission of Syrian refugees at the federal level. If Obama doesn't do so, he will likely continue to face political pressure. But there's not much worry at this point about being able to shelter the refugees: DHS has identified 180 cities and towns across the country that are willing to accept them. (For what it's worth, the agency also plans to focus on women and children, those with medical conditions, and survivors of violence and torture.)

Interestingly, it might not be impossible to implement the proposal from Bush and Cruz to accept only Christian refugees. Leopold noted that religious faith can already be a reason for an applicant to seek refugee status in places where certain religions are persecuted.

"If someone claims persecution on account of being a Hindu in a Muslim country or something like that," he said, "they are tested in terms of their knowledge of their own religion. That's one of the tests of truthfulness and veracity." The USCIS has techniques of trying to suss out how honest an applicant is being in identifying his religion (or, for that matter, his political beliefs) meaning that adding a religious test, for all of the political questions, could be possible. "What you can do is ask for details and circumstances to create a composite of somebody and make a determination as to whether or not they are telling the truth when they say they of a certain faith or religion." In the past, Congress has enacted laws blocking immigrants based on nationality. Barring refugees based on faith, Leopold suggests, "raises a whole host of legal, political and humanitarian concerns."

None of this is foolproof. "You can never know what's in someone's head," Leopold added. "But you can know what they've done or who they've associated with or who their family members are. All of that is very testable through the systems in place."

He added a personal appeal. "I have been representing Syrian clients since 2011," he said. "Sitting in my office, I have never seen a consistent group of people with such a palpable fear of going back to their home country. I've never seen the kind of relief on faces as when their asylum is granted."

Which demonstrates the challenge. There are unquestionably frightened Syrians who need to escape violence and fear in their home countries or in refugee camps. But there are also frightened Americans who saw what happened in Paris and worry about it happening here.

Only the latter group votes.

This post has been updated.