Illegal border crossings from Mexico dropped by 7 percent last month, the second straight monthly decline, but some experts questioned whether it represents a meaningful improvement or simply reflects the natural ebb and flow of illegal migration.

The Department of Homeland Security (DHS) reported Wednesday that U.S. Border Patrol agents apprehended 31,303 illegal immigrants in July. Customs and Border Protection officials deemed another 8,650 people “inadmissible” after they tried to sneak or cheat their way through border crossings facilities.

Experts closely watch apprehension statistics for a gauge of overall illegal immigration, with a rule of thumb holding that roughly one border crosser makes it into the United States for every one caught.

Taylor Houlton, the DHS press secretary, hailed the new numbers as a sign that the administration is making progress after illegal crossings spiked earlier this year.

“This decrease shows that when there are real consequences for breaking the law, the conduct of those considering crimes will change,” he said in a statement. “In the month of July, we saw a decrease in illegal border crossings because human traffickers and transnational criminal organizations were put on notice that this administration was increasing prosecutions of those entering the country illegally.”

But Brandon Judd, president of the U.S. Border Patrol Council, said the change from June to July was not substantially different from what occurred during President Barack Obama’s administration. He noted that overall apprehensions last month were higher than in July of 2015 and 2012.

“What we’re seeing is the exact same trend year in and year out,” he said. “My main concern is that the numbers in July 2018 … exceeded the numbers of two of Obama’s last four years in office.”

President Donald Trump presided over an immediate and steep drop in illegal immigration when he took office after a campaign run primarily on the promise of cracking down on cross-border lawbreaking. Border apprehensions plummeted 63 percent from January to April last year, hitting a low of 15,766.

Judd said DHS failed to take advantage of a golden opportunity to follow up with changes on the ground.

“President Trump drove illegal border crossings to a 45-year low, and then we failed to enact any policies that would have kept it going,” he said.

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Judd added that in April 2017, “we were screaming and yelling for a zero tolerance policy … Instead, we waited. We waited until the numbers got too high.”

That month, according to DHS statistics, 81 percent of illegal immigrants arrested were single adults. Judd said a zero tolerance policy of bringing criminal charges against first-time border crossers could effectively have been implemented because all of them could have been jailed.

By the time the policy finally came this April, Judd said, the numbers simply were too high. The government lacked the bed space to carry out the policy. He estimated that only about 15 percent of illegal immigrants crashing the border are subjected to prosecution.

“That’s a far cry from zero tolerance,” he said.

Judd said that implementing the policy a year ago would have both sent a clear message to people in Central America who were thinking about making the journey and avoided the politically damaging specter of separating illegal immigrants traveling with children.

Jessica Vaughan, director of policy studies at the Center for Immigration Studies (CIS), said border crossing numbers typically have been flat in June and July over the past few years. So a drop in 2018 is welcome, she said.

“It’s typical for it to be more level in this part of the summer, coming down from the spring high, so to speak,” she said. “This looks like good news.”

But Vaughan cautioned, “We have to see if it’s sustained.”

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Vaughan said part of the reason for the decrease could be that publicity of the family separations could have had a deterrence effect. Although Trump ended the policy with an executive order in June, Vaughan said there is a lag both because it takes time for word to filter down to Central America and because the journey takes so long.

It is possible that border crossings will rise again in the coming months as news of Trump’s reversal gets back to Central America, Vaughan said. Talk of codifying the quasi-amnesty Deferred Action for Childhood Arrivals (DACA) program also could serve as a magnet, she said.

“We’re not going to know for sure for a few months,” she said.