– The number of people taken into custody along the U.S. southern border fell 28% in June, a drop that U.S. authorities say reflects the early impact of Mexico's crackdown on Central American migration.

Border crossings typically rise in the spring and slump during the scorching summer months, but the drop registered from May to June was significantly larger than in previous years, according to Homeland Security statistics released Tuesday. U.S. authorities detained 104,344 along the border last month, down from 144,278 in May.

June was the fourth month in a row that border arrests exceeded 100,000, and the total was more than twice the 43,180 taken into custody in June 2018 and a nearly fivefold increase over June 2017, when authorities detained 21,673.

President Donald Trump has treated the monthly U.S. Customs and Border Protection arrest totals like a stock index for the success of his immigration policies, periodically erupting in fury at Homeland Security officials as the numbers soared to a 13-year high.

In late May, with holding cells along the border overflowing and Central American migrants streaming across in groups of as large as 1,000, Trump forced emergency negotiations with Mexico by threatening to impose potentially crippling tariffs — a political gambit aimed at shifting responsibility for the border crisis to a foreign government.

The move spurred immediate action: Leftist President Andres Manuel Lopez Obrador's administration persuaded Trump to delay the economic penalty by promising that Mexico would dramatically increase enforcement efforts and work with the United States to overhaul regional asylum policies.

Mexico's response

Mexico has since deployed thousands of national guard troops to patrol its borders and stop migrants traveling along railways and roads, at times grabbing families just steps from U.S. soil along the banks of the Rio Grande. Mexico said it has increased deportations 33% since the deal.

"The reduction in apprehensions accounts for decreases across all demographics, including unaccompanied minors, family units and single adults, as well as decreases in migrants from all Northern Triangle countries, particularly those coming from Guatemala," the Department of Homeland Security said in a statement.

"Decreasing apprehension numbers will provide greater opportunities for the DHS to address capacity challenges for those in custody and speed the movement of unaccompanied children into Health and Human Services (HHS) care," the department said.

The drop in border crossings has allowed for a bit of a reprieve for U.S. border stations, which officials say have been brought back from "the breaking point," allowing U.S. agents to improve care and processing times for children and families following a wave of anger over images of migrants packed into squalid cells and reports of mistreatment. The number of children in CBP custody has fallen from more than 2,500 in early June to fewer than 350 in recent days, DHS officials said this week.

U.S. Customs and Border Protection officials says the number of migrants its custody has dropped more than 40%, but the agency it still has about 10,000 in holding cells and stations designed for half that many people.

While it likely will take months to see whether Mexico's enforcement efforts will have a sustained effect on migration, the one-month dip also could just as easily reverse.