U.S. Border Patrol apprehensions of illegal immigrants and foreigners deemed “inadmissible” at border-crossing stations dropped by 16 percent from May to June, a decline that officials attributed to the zero-tolerance policy implemented in April.

Border Patrol officers caught 34,114 illegal immigrants in June, down from 40,338 in May. That June number included 5,115 children traveling alone and another 9,449 adults traveling with children. Both numbers also were lower than in May.

Experts closely track border apprehensions as a way to measure illegal immigration.

Department of Homeland Security (DHS) press secretary Taylor Houlton attributed the June drop to a policy implemented in April of filing misdemeanor criminal charges against first-time illegal border crossers. That policy is mandated under the law but was previously rarely followed.

“DHS will continue to enforce the rule of law and uphold our nation’s immigration laws as passed by Congress,” Houlton said in a statement. “As we have said before, the journey north is dangerous and puts individuals in the hands of smugglers and traffickers. We continue to call on Congress to address the crisis at the border by closing legal loopholes that drive illegal immigration.”

Some experts, however, questioned the impact of the zero-tolerance policy or the decision in April to deploy the National Guard to the border. Jessica Vaughan, director of policy studies at the Center for Immigration Studies (CIS) — which favors stricter border enforcement — noted that the illegal immigration trend line tracks almost exactly the apprehension patterns in 2016.

“In this particular instance, I think it’s hard to separate the policy change from traditional seasonal changes,” she said. “I think it’s too early to say if it’s going to be significant.”

Border crossings plummeted to abnormally low levels immediately after Trump took office last year, reaching a low point of 15,766 in April 2017. But the numbers eventually rebounded.

In an attempt to deter families traveling with children, the administration began applying zero-tolerance policies toward border crossers even if they had children with them. That meant sending parents to detention centers and children to care facilities run by the Department of Health and Human Services (HHS).

But the separation of families sparked a massive backlash, and Trump last month signed an executive order ending the practice. Instead, the administration has pursued options for detaining parents and children together until their court dates arrive. Some immigration advocates have called for resurrecting a program that supervised illegal immigrant families and encouraged them to show up for immigration court hearings.

Who do you think would win the Presidency?

By completing the poll, you agree to receive emails from LifeZette, occasional offers from our partners and that you've read and agree to our privacy policy and legal statement.

Trump on Thursday renewed his call for congressional action, tweeting that illegal immigrants need to get off America’s “front lawn.”

Vaughan said the numbers do not indicate that the policies have had a huge deterrent on families entering the country illegally. The number of adults traveling with children caught by Border Patrol dropped from 9,485 to 9,449 in June.

“It looks like it was having a good impact on overall crossings,” she said. “But it doesn’t seem to have as much impact on family crossings.”

Related: Trump Demands Congress Tell Illegals to Get Off Our Lawn

The number of foreigners deemed inadmissible at ports of entry dropped from 11,567 to 8,451 — a 26.9 percent reduction. Vaughan attributed that steep decline to a policy of prescreening foreigners on pedestrian bridges and other roads leading to customs outposts just inside the border.

Those screeners turned away foreigners who did not have visas or other travel documents, so they were not counted in the statistics of foreigners deemed inadmissible.