The shift was evident Tuesday in the Rio Grande Valley of South Texas, which has been one of the border’s busiest migration corridors for the past decade. Along areas of the border where migrant families have crossed in large groups to surrender to U.S. authorities and seek protection, Border Patrol agents pursued a handful of adult men trying to evade capture. Agents’ radios were mostly quiet.

It is not unusual for agents to see a short-lived decline in crossings whenever the government announces a major crackdown. Illegal entries soared to record levels late last year but have been trending downward over the past several months, in part due to more aggressive enforcement by the Mexican government.

But Biden administration officials are hoping the falling numbers can blunt Republican criticism of the president’s border record as he prepares to face off in a debate Thursday with likely GOP nominee Donald Trump. Polls consistently show high rates of disapproval with Biden’s handling of border security and immigration issues.

Homeland Security officials cautioned the results of the crackdown were preliminary, and cast the measures as an attempt to balance tougher enforcement with more generous opportunities for migrants to reach the United States legally.

Biden has “carried out the largest expansion of lawful pathways and orderly processes in decades,” the DHS statement read, measures that are “freeing up the asylum system for those with legitimate claims.”

The American Civil Liberties Union and immigrant advocacy groups are suing to block Biden’s asylum restrictions.

U.S. immigration laws allow anyone who reaches U.S. soil to seek humanitarian protection if they have a well-founded fear of persecution or grave harm in their home country. The emergency measures Biden announced June 4 suspend access to those protections on an emergency basis, arguing the U.S. immigration system is too overwhelmed by illegal crossings and insufficient resources.

Biden’s measures call for the asylum restrictions to lift if illegal crossings average fewer than 1,500 per day. They would return if the levels once more surpass 2,500 daily.

Lower number of illegal crossings have allowed U.S. agents to better safeguard the border and increase patrols, the department said, “enhancing DHS efforts to interdict individuals who pose a threat to public safety.”

The DHS statement echoed the administration’s calls for lawmakers to boost funding for the U.S. immigration system, including a major expansion of detention and deportation operations.

DHS said the number of migrants who are allowed into the United States with a pending court date after crossing illegally — the practice derided as “catch and release” — has dropped 65 percent under Biden’s measures. Deportations and returns to Mexico have doubled over the past three weeks, the department said.