America’s illegal immigrant population fell to 10.8 million in 2016, the lowest mark since 2003, according to a study released Thursday by a New York-based think tank.

The Center for Migration Studies (CMS), which used Census Bureau data to make the estimate, argued the falling numbers undercut the need for the border wall President Donald Trump has proposed.

“We shouldn’t have illegal immigration. We should have better immigration policies,” the report’s author, Robert Warren, told LifeZette. “Building a ‘big ol’ wall’ is a sign of a failed immigration policy.”

The report estimates that the unauthorized population shrank from 11.7 million in 2010 to just under 10.8 million in 2016, a 1 percent decrease. Warren, a former Census Bureau demographer who now is a senior visiting fellow at the think tank, told LifeZette that the decline means the number of illegal immigrants returning home, dying, or adjusting to legal status has outpaced the number of new illegal immigrants coming here in recent years.

Warren noted that the federal government doubled the number of Border Patrol agents under former President George W. Bush. In addition, he said, an improved economy and lower birth rate in Mexico has led fewer people to come to the United States from there.

“It just happened that those two trends crossed [back] in 2008,” he said.

After hitting 6.6 million in 2010, the number of illegal immigrants from Mexico shrank to 5.66 million in 2016, according to the report.

Some advocates of tighter border security greeted the study’s conclusions with skepticism. The most recent estimate by the Federation for American Immigration Reform (FAIR) pegs the number at 12.5 million. Matthew O’Brien, director of research at the think tank, said he believes many estimates of the illegal immigrant population fail to adequately measure the undercount that comes from surveys.

“They make a lot of presumptions,” he said.

Steven Camarota, director of research at the Center for Immigration Studies (CIS), said the report’s estimates seem reasonable. But he said CMS overstates the meaning.

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“They get small changes and they attribute a lot to it,” he said. “It’s not statistically significant … They really want to tout this decrease, and it’s not clear it’s meaningful.”

[lz_table title=”Illegal Immigration Dropping?” source=”Center for Migration Studies”]Illegal immigrants in the U.S.
1990,3.5 million,2.04 million
2000,8.6 million,4.997 million
2010,11.725 million,6.6 million
2016,10.79 million,5.66 million

Eric Ruark, director of research at the advocacy group NumbersUSA, also said he believes the true number is higher. But even it if is accurate, he added, that is not a good argument against tougher immigration enforcement. He said more aggressive enforcement under former President Barack Obama could have driven the number much lower.

“It’s still almost 11 million and within that framework, it may be over 11 million,” he said. “What if we had not sent the signal during the Obama administration [that] if you come [here] and you don’t kill someone, you can stay?”

Warren, the study’s author, said the numbers suggest that greater border security would be ineffectual; the vast majority of illegal immigrants have been in America for years. Many have U.S.-born children and deep roots, he said.

“Most of these 11 million have been here for 10, 15 years,” he said. “They’re not going anywhere.”

Ruark agreed border security alone is insufficient. He said illegal immigration calls for a comprehensive approach, including mandatory use of the E-Verify system to confirm the legal status of newly hired employees.

“Until you hold employers accountable, all you’re going to do is tread water,” he said.

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Camarota said the fact that more illegal immigrants are leaving than coming does not mean the border is secure.

“If these numbers are right, it still means hundreds of thousands of people are successfully sneaking across the border every year,” he said.

“Frankly, 10 million vs. 12 ½ versus 20 million really doesn’t make that much difference,” he said.

O’Brien, of FAIR, said the problems caused by illegal immigration are more important than the precise number.

“Frankly, 10 million vs. 12 ½ versus 20 million really doesn’t make that much difference,” he said.

PoliZette senior writer Brendan Kirby can be reached at [email protected]. Follow him on Twitter.