The Trump administration is decrying a 'surge' of illegal immigration - even though border-crossing arrests are at historic lows

Associated Press/Evan Vucci

President Donald Trump listens during a meeting with Baltic leaders in the Cabinet Room of the White House, Tuesday, April 3, 2018, in Washington.

• President Donald Trump on Wednesday moved to deploy the National Guard to reinforce the US-Mexico border.
• But government data show the number of people arrested while trying to illegally cross the border is hovering near the bottom of a decades-long downward trend.
• Small upticks have occurred month to month, and the Trump administration says the increase in arrests between the fiscal years 2017 and 2018 are cause for concern.

President Donald Trump on Wednesday authorized the deployment of National Guard troops to the US-Mexico border, amid what his administration called a "drastic surge of illegal activity on the southern border."

Immigration advocates criticized the move as unnecessary, but the Trump administration and others were quick to point out that the National Guard has been deployed to the border in the past - most recently by former presidents Barack Obama and George W. Bush.

It's unclear when the troops will be deployed, what they'll cost, and how exactly they'll be put to use. Trump said Thursday he planned to send between 2,000 and 4,000 troops.

Federal law prohibits them from enforcement activities such as detaining immigrants, but the National Guard has been used in the past for tasks like surveillance and fence construction. Trump said the troops would "probably" stay until the wall is built.

The Trump administration has cited criminal activity such as human smuggling and drug trafficking as reasons to crack down on the border, but Trump himself has appeared preoccupied with a "caravan" of central American migrants, some of whom intended to travel through Mexico to the US border and either seek asylum or cross the border undetected.

Trump's top Cabinet officials, too, have characterized illegal border-crossing as a particularly critical issue requiring immediate attention.

"We will not allow illegal immigration levels to become the norm - more than a thousand people a day, 300,000 a year," Homeland Security Secretary Kirstjen Nielsen said Wednesday. "Violating our sovereignty as a nation will never be acceptable to this president."

But despite the Trump administration's call for urgency, data from the Customs and Border Protection agency actually show that arrests for illegal border crossing has been falling for years and now hovers near the bottom of a 40-year low.

Here's what the trend looks like:

Business Insider/Shayanne Gal

Annual southern border arrests between 2000 and 2017.

Despite this, the Trump administration has expressed alarm at an uptick in southern border apprehensions in recent months.

Senior administration officials told reporters on Wednesday that the border apprehension data for fiscal year 2018 show a significant increase between February and March, as well as a "staggering increase" from the previous year.

Indeed, border apprehensions in fiscal year 2017 dropped so low that authorities only recorded 16,588 arrests that March. This year, they recorded 50,308 - a significant uptick, but one that still remains relatively low in the context of the past four decades.

Here's what the data look like for this year, illustrating the uptick the administration is concerned about:

Business Insider/Shayanne Gal

Illegal border crossing arrests in Fiscal Year 2018.