Read: Why migrant caravans keep forming

U.S. and international law would dictate that the migrants have the right to apply for asylum once they’re inside the U.S. But a deal designed to keep asylum seekers in Mexico would make it difficult, if not impossible, for them to successfully present their case before an immigration judge, according to legal experts.

“I do not see a way to do this that will enable the United States to honor its own U.S. laws that guarantee asylum seekers the right to seek asylum,” said Greg Chen, the director of government relations for the American Immigration Lawyers Association.

There are a number of problems that could arise, according to Chen. For one, applying for asylum is an arduous process that’s made easier by the guidance of legal counsel, and it would be difficult for an American lawyer to provide assistance if clients are in Mexico. “If you can’t meet with your counsel, it’s almost impossible to provide counsel,” he said. Conversations over the phone, which could be seen as an alternative, might also prove difficult, given asylum seekers’ potentially limited phone access. There’s also the challenge of obtaining documents to corroborate asylum claims, which, while not required, can significantly help a case. Attorneys often help their clients with that task as well.

Lawyers have proved critical in immigration-court processes, particularly in asylum cases, where the burden is on individuals to prove that they’ve been persecuted or have a “well-founded fear” of future persecution in their home country. Research has also shown that immigrants who have representation in court are more likely to succeed in their cases.

Still, the asylum process is long—and the success rate is low. Immigration courts have been bogged down for years: The backlog of cases stands at more than 760,000, and court appearances are often scheduled months, if not years, in the future. And only a fraction of those who pass the credible-fear screening are granted asylum: According to the Department of Homeland Security, less than 10 percent of those who applied were deemed qualified in the past year.

Legal obstacles aside, there’s also the matter of whether migrants will be safe and self-sufficient while remaining in Mexico indefinitely.

Lee Gelernt, the deputy director of the ACLU’s national Immigrant Rights’ Project, told me that any proposal that doesn’t guarantee migrants’ safety or afford them the “same full immigration hearings they would’ve received in the U.S.” is a “nonstarter legally.”

Read: There is no easy way for Trump to stop the latest caravan

Alex Nowrasteh, a senior immigration-policy analyst at the libertarian Cato Institute, noted that migrants would have to secure work authorization in Mexico, because “they’d have to be able to support themselves while they’re waiting for asylum.” The Trump-Mexico deal “sounds like a system basically designed to turn away as many asylum seekers as possible,” Nowrasteh said, “to make it difficult for those who remain, and to approve as few as possible.”