Republican nominee Donald Trump's call for "extreme vetting" of immigrants as a way to guard against terrorism in the U.S. has a long history and hints at broad promises and potential risks.
A screening test for potential immigrants goes back decades to when the U.S. sought to exclude people associated with anarchism or communism, said Hiroshi Motomura, professor of law at the University of California, Los Angeles and author of Immigration Outside the Law.
"It intensified during the Cold War, but it's been on the books on American immigration law really for over a century," said Motomura.
But there's an important difference to Trump's proposal, said Motomora, one that could lead to "unintended consequences."
"The difficulty is once you go beyond these organizational affiliations and past acts that people have committed, then you're really trying to read the minds of people as to what they may want to do in the future and that leads to a lot of questions as to exactly how that would be implemented," he said.
It could also lead to the immigration system being vulnerable to prejudices, as local officials wield greater power in an effort to define broad terms, such as "values" and "respect," to determine which candidates to accept or reject.
"You're sitting as the Secretary of State in Washington, D.C, and you don't really know what's going on," said Motomura. "Ultimately, it means these decisions are likely to be made on these subjective prejudices."
Speaking in Youngstown, Ohio yesterday, Trump said that his system would "only admit into this country those who share our values and respect our people."