Biden Shut the Border to Asylum Seekers. The Question Is Whether the Order Can Be Enforced.

There are still ways for people to cross the U.S.-Mexico border illegally, particularly without any new resources to help guard the 2,000-mile frontier.

As of 12:01 a.m. on Wednesday, the U.S. border with Mexico was shut down to nearly all migrants seeking asylum in the United States.

The drastic action, the result of an executive order signed by President Biden, was designed to keep the border closed at least through Election Day and defuse one of the president’s biggest vulnerabilities in his campaign against former President Donald J. Trump.

The question is how broadly it can be enforced, especially along a 2,000-mile border that does not have nearly the capacity to manage the number of people who want to enter the United States.

As of Wednesday morning and into Thursday, the order appeared to be working, although it was still too early to make a real assessment. Migrants in the border towns of Mexicali and Ciudad Juárez were being turned away, and the word was spreading.

In Mexicali, Guadalupe Olmos, a 33-year-old mother, said that when she heard about the new policy, she wept, and said it was now pointless to try to enter the United States. Last year, she said, gunmen shot up her car, killing her husband. She and her three children survived and have been trying to get out of Mexico.

“It is not going to happen anymore,” Ms. Olmos said. “Yesterday, they told us that this is over.”