President Donald Trump moved Wednesday to deploy the National Guard along the U.S. southwest border with Mexico.

And Secretary of Homeland Security (DHS) Kirstjen Nielsen offered three statistics to explain why.

The data Nielsen offered during a news conference at the White House show how dramatically the nature of illegal border crossings has changed over the past decade:

Before 2009, 90 percent of illegal immigrants who crossed the border were Mexicans. Today, nearly 50 percent come from Central America.

Before 2011, 90 percent of border crossers were single men. Today, roughly 40 percent are families with children.

Before 2013, one out of every 100 border crossers claimed political persecution in their home countries. Today, that ratio is one out of 10.

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These data give a clear indication that smugglers are aware of weaknesses in the U.S. immigration system and are exploiting them, Nielsen said.

“Smugglers themselves are gaming the system — pure and simple,” she said. “They take advantage of the loopholes in our laws. They know that we cannot prosecute as we need to [in order] to stop their behavior.”

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Trump’s decision to call out the National Guard comes days after he sparked controversy by suggesting a military role in border security. Nielsen said the details of the administration’s plan have not been worked out, but she added that officials have consulted with border state governors.

Nielsen said the administration hopes to deploy Guardsmen as soon as possible but would only say the number would be as many as necessary. She suggested the operation likely would resemble previous border deployments in which Guard members provided support for U.S. Border Patrol officers.

The emerging plan drew plaudits from security hawks inside and outside of Congress.

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“I fully support President Trump’s use of our military to secure the border against invasion by foreign nationals … For too long, illegal aliens have exploited weak laws and then sought and sometimes gained de facto permanent legal status at great cost and damage to American taxpayers,” Rep. Mo Brooks (R-Ala.) said in a statement.

Ira Mehlman, a spokesman for the Federation for American Immigration Reform (FAIR), praised the move.

“It’s certainly a necessary step given escalating levels of illegal immigration coming across the southern border … But this is really stopgap,” he said.

Not all immigration hard-liners were impressed, however. William Gheen, president of the Americans for Legal Immigration Political Action Committee, dismissed the move as a stunt much like past National Guard deployments by former presidents Barack Obama and George W. Bush.

“Rehashing Bush’s failed policies by sending the National Guard to the border to wash vehicles, answer phones, fix fences, and grill burgers for the Border Patrol shows the Trump administration is more interested in appearances than in actually stopping illegals from entering the U.S.,” he said in a statement.

But Trump administration advisers insisted that the National Guard is only one piece of a comprehensive strategy. A senior official, briefing reporters on condition of anonymity, said the White House is preparing proposals to streamline deportations.

“I do think it will be effective. The National Guard can do everything Border Patrol can except make arrests.”

“We are going to be sending Congress a legislative package to close these loopholes so that we can return illegal immigrants in a responsible and expeditious manner, and our expectation will be for rapid action on that legislation in the House and Senate,” he said.

The Trump administration tried and failed to broker a deal earlier this year that would involve some of those same measures in exchange for amnesty for illegal immigrants brought to America as children.

But the official told reporters that the White House might enjoy more success with legislation that is narrowly tailored.

“The more that you are focused on a single objective, the easier it is to marshal and rally support behind a particular proposal in today’s divided and fractured Congress,” he said.

Nielsen argued that the new action is needed because the “Trump Effect” — a steep decline in border crossings that followed the president’s inauguration — eventually evaporated as smugglers and transnational criminal organizations realized that policy changes did not match the rhetoric.

Mexico has no obligation to accept Central Americans. It makes removing them from the United States more difficult, Nielsen said.

The demographic changes that have occurred among illegal immigrants is important, Nielsen said, because U.S. law makes it harder to deport non-Mexicans. Under current statutes, U.S. Border Patrol agents who apprehend Mexicans near the international boundary can turn them back to the Mexican government.

But Mexico has no obligation to accept Central Americans. It makes removing them from the United States more difficult, Nielsen said.

The same goes for children caught near the border. Court rulings have barred the federal government from detaining minors long term. That has forced a continuation of the catch-and-release policies implemented during the Obama administration.

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Illegal immigrant children arriving at the border from Central America get a free ride at U.S. taxpayer expense to relatives in America. Many disappear before backlogged immigration courts can resolve their cases.

“We have seen the smugglers advertise this as an enticement, and we have seen smugglers, unfortunately, fraudulently use children to gain entry into our country,” Nielsen said.

Jessica Vaughan, director of policy studies at the Center for Immigration Studies (CIS), said the impact of deploying the National Guard should not be underestimated.

“I do think it will be effective,” she said. “The National Guard can do everything Border Patrol can except make arrests.”

With guardsmen providing aerial surveillance, repairing fencing, moving prisoners and performing other duties, it frees up more Border Patrol officers to find and arrest illegal immigrants, Vaughan said.

“It’s a big force multiplier, and it’s a deterrent,” she said.

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