Nidia Montenegro fled violence and poverty at home in Venezuela, survived a kidnapping as she traveled north into Mexico, and made it to the border city of Tijuana on Sunday for a U.S. asylum appointment that would finally reunite her with her son living in New York.

STORY: As U.S. President Donald Trump took office on Monday and began a sweeping immigration crackdown, migrants waiting in Mexico nervously checked the U.S. government app known as CBP One. The program had allowed hundreds of thousands of migrants to enter the U.

The CBP One app that worked as recently as that morning would no longer be used to admit migrants after facilitating entry for nearly 1 million people since23.

President Donald Trump signed executive orders Monday to beef up security at the southern border that began taking effect hours after he was inaugurated, making good on his defining political promise to crack down on immigration and marking another wild swing in White House policy on the divisive issue.

The actual execution of such a far-reaching immigration agenda is certain to face legal and logistical challenges.

Nidia Montenegro, a Venezuelan woman seeking asylum, reached the U.S. border in Tijuana only to find her long-awaited appointment canceled amid President Trump's national emergency declaration. Thousands face similar despair as border policies shift,

The president moved quickly to cancel the CPB One app, which allowed migrants to schedule appointments to gain entry into the United States, turning away potentially tens of thousands of migrants.

The Trump administration Monday ended use of a border app called CBP One that has allowed nearly 1 million people to legally enter the United States with eligibility to work.

WASHINGTON (AP) — President Donald Trump’s promises to beef up security at the southern border with Mexico began taking effect soon after he was inaugurated Monday, making good on his defining political promise to crack down on immigration and marking another wild swing in White House policy on the divisive issue.

Kenneth Genalo, director of U.S. Immigration and Customs Enforcement's New York City field office, holds an information sheet on Wilmer Patricio Medina-Medina

The Trump administration has ended use of the border app called CBP One that allowed nearly 1 million people to legally enter the United States.