As US election nears, Mexico keeps up border enforcement, blocks migrants.

Migrant encounters at the U.S. border plunged from nearly 250,000 in December of last year to below 60,000 last month .

Mexico 's immigration agency reported a 160% increase in migrant encounters through the first seven months of this year .

Illegal border crossings have been at the center of Republican Donald Trump's campaign.

The U.S. delegation came with "specific asks" for Mexico , senior State Department officials say.

They included increased migration enforcement on cargo rail and passenger bus lines and for Mexico to "decongest" its northern border with the United States .

Mexico 's economy takes a direct hit with every slowdown in cross-border commercial traffic.

The Biden-Harris administration reassigned customs officers to help Border Patrol process migrants.

The U.S. isn't paying for Mexico 's migration enforcement programs, according to State Department officials.

The first two years of the Biden administration produced record highs in migrant encounters, more than 2 million each year in 2021 and 2022 .

The number of migrants encountered by Border Patrol agents dropped in half immediately after cabinet secretaries rushed to Mexico City .