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.

The Tucson area in the Arizona desert saw a similar decline in unlawful crossings, DHS Secretary Alejandro Mayorkas said during a news conference in that border city Wednesday.

"The president's actions are working because of their tough response to illegal crossings," Mayorkas said. "We are attacking the smuggling organizations that prey on the vulnerable even as the smugglers try to undermine our actions."

Biden administration officials hope the falling numbers of migrants can blunt Republican criticism of the president's border record. The president has criticized Republicans for opposing a bipartisan bill that would have increased enforcement, leaving him to act on his own.

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.

Regardless of where one falls, the facts remain that the Congressional GOP negotiated a border security deal that they said was better than anything before it, but they allowed Trump to force its defeat for the sake of his own campaign. Hopefully Biden will contrast himself as the President trying to fix the problem compared to Trump being the candidate trying to exploit the problem for his own benefit, the country's needs be damned.

U.S. immigration laws allow anyone who reaches U.S. soil to seek humanitarian protection if they have a well-founded fear of persecution 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.

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.