Thousands of foreign nationals are waiting south of the U.S.-Mexico border to claim asylum.

The backlog is a direct result of the Trump administration’s efforts to clamp down on burgeoning asylum claims.

Approximately 13,000 people are on waiting lists to claim asylum in the U.S., an Associated Press investigation found. The AP determined the amount after traveling to eight Mexican cities dotted along the border. Tijuana, the city with the longest line, had 4,800 people on the wait list. Ciudad Juarez and Nogales were two other cities with major lines, with 4,500 and 1,000 people, respectively, waiting to get into the U.S.

The backlog is a consequence of the U.S. government controlling how many people can claim asylum a day, a process known as “metering.”

Each day at ports of entry, Customs and Border Protection (CBP) officers communicate with their Mexican counterparts, telling them how many immigrants are allowed to cross the border. Officials who handle the massive wait lists then direct the chosen individuals to cross the border to make their asylum claims.

The metering process — which has sparked intense ire from progressive and Democratic circles — has allowed the U.S. government to somewhat manage the massive numbers of immigrants applying for asylum. In a major win for President Donald Trump’s immigration agenda, the Ninth Circuit Court of Appeals ruled Tuesday that he has the authority to send asylum applicants to Mexico as they wait for their claims to be adjudicated.

The White House has moved forward with a number of other directives aimed at curbing the onslaught asylum claims.

Border Patrol will soon undergo training to conduct on-the-spot asylum interviews themselves, giving relief to immigration courts and expediting the process for those who would otherwise be deported. Asylum screeners have been ordered to get tougher and more skeptical with applicants as they seek to weed out fraud. (RELATED: Self-Deportations Are Rising Dramatically Under Trump Administration)

In one of its latest bids to deter asylum seekers, the Trump administration is seeking to charge immigrants for lodging asylum claims and require immigration courts to settle cases within 180 days.

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