The Trump administration on Monday abruptly closed down a government program created by the Biden administration to allow migrants to use an app to secure an appointment for admission into the United States through legal ports of entry, signaling the start of President Trump’s promised crackdown at the southern border.

Moments after Mr. Trump took the oath of office, an announcement posted on the CBP One program’s website declared that the app would no longer function and that “existing appointments have been canceled.”

The program, which debuted in early 2023, allowed 1,450 migrants a day to schedule a time to present themselves at a port of entry and seek asylum through U.S. immigration courts. More than 900,000 migrants entered the country using the app from its launch in the beginning of 2023 to the end of 2024.

A former Department of Homeland Security official who spoke on the condition of anonymity said that around 30,000 migrants had appointments to enter the United States through the app as of Monday morning.

At the El Chaparral border crossing in Tijuana, Mexico, dozens of migrants who stared at their phone screens trying to check whether their appointments were still valid instead found the crushing message that they no longer existed.

“I am in shock,” said Maura Hernandez, who received the news on Monday morning as she arrived in Tijuana with her four small children from the state of Michoacán. She had a scheduled appointment on Tuesday.

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