In defending his failed, unilateral attempt to grant de facto amnesty to millions of illegal immigrants, struck down Thursday by the Supreme Court, President Obama bragged that he has largely sealed America’s leaky border with Mexico — even as immigration experts are sounding warning cries about a fresh wave of crossings.

Speaking after the Supreme Court decision upholding the block on his executive amnesty — at least for the time being — Obama lamented that Congress has never passed a law providing a path to citizenship for illegal immigrants, and he claimed that more border patrol agents and better technology has stemmed the flow of illegal immigrants from Mexico.

“We don’t really know, because all we know is how many get caught … We don’t even know if apprehensions are a reliable measure of how many try to come.”

“That has helped cut illegal border crossings to their lowest levels since the 1970s,” he said. “It should have paved the way for comprehensive immigration reform.”

Critics of the president’s immigration polices say the claim is both dubious and irrelevant. How can Obama know how many people come to the country illegally?

“We don’t really know, because all we know is how many get caught,” said Jessica Vaughan, a former foreign service officer who now serves as director of policy studies at the Center for Immigration Studies. “We don’t even know if apprehensions are a reliable measure of how many try to come.”

It is that metric — border apprehensions — on which Obama likely bases his claim. It is true that those have declined sharply during his presidency. According to Customs and Border Protection statistics, agents apprehended 337,117 people in fiscal year 2015, a 39 percent decrease from the 556,041 caught in fiscal year 2009. That continues a trend that predates Obama. In fiscal year 2000, border patrol officers nabbed almost 1.7 million people.

Congressional testimony indicates that for every illegal immigrant caught at the border, one slips through. So it is reasonable to assume that border crossings have declined. But Vaughan questioned the logic that decreased apprehensions argues in favor of comprehensive immigration reform.

“I think they are a lot lower than they used to be, but I don’t know [if] that leads to a call for amnesty,” she said.

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Vaughan said just as important as that number is what happens to illegal immigrants who are caught. The policy of Obama’s Department of Homeland Security is to free anyone who claims — no matter how implausibly — to have been living in the United States prior to Jan. 1, 2014. More recent arrivals who seek asylum or challenge their status in some other way are often released with instructions to appear for an immigration hearing. The acting chief of the U.S. Border Patrol testified before the Senate last month that 40 to 55 percent of them fail to show up for those hearings.

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Sen. Jeff Sessions said in a floor speech Thursday that border apprehensions are up so far this fiscal year.

“Total apprehensions of all illegal aliens appears to be on the rise, which is an indice of increased illegality into this country,” he said.

[lz_table title=”Border Apprehensions” source=”U.S. Customs and Border Protection”]Fiscal year,Apprehensions
2008,723.8K
2009,556K
2010,463.4K
2011,340.3K
2012,364.8K
2013,420.8K
2014,486.7K
2015,337.1K
[/lz_table]

Sessions said Obama “effectively eliminated whole sections” of immigration law — while ruining the morale of border agents.

“They have been ordered not to do their duty,” he said. “They put their lives on the line … and they arrest people and bring them in. And what happens? They’re not deported. They’re released on bail or some sort of promise to appear and go into the country, as they plan to do all along.”

Sessions pointed to another statistic, which tracks “family units” arriving at the Southern border from Central America. That refers both to unaccompanied minors and children with adults. The number spiked in 2014, declined last year and now is rising again.

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“We’ve seen an increase in lawlessness in recent years,” he said, “And in fact, it looks like this year, among a number of categories, we’ve already recorded the same level of arrests that we did in all of the last fiscal year.”

Vaughan said reducing border crossings does nothing to control illegal immigration if foreigners simply adopt other ways of coming into the country. Experts believe a greater share of illegal immigrants now enter legally on a visa program and then become illegal immigrants once those visas expire.

A Center for Immigration Studies report this month estimated that 1.1 million new illegal immigrants entered the United States in 2014 and 2015, an increase from the 700,000 who came in the previous two-year period. Vaughan said the trek across Mexico has become more dangerous and often requires payments to smugglers, which has reduced the flow.

“It’s definitely not down because people are afraid they’re going to get caught,” she said.