Customs and Border Protection (CBP) announced late Tuesday that it encountered more than 178,000 migrants in April, a slight increase to the high numbers of March -- but a more than 900% increase over April of last year, putting into context how dramatically the numbers have spiked in recent months.

CBP encountered 178,622 migrants in April trying to enter the U.S., a 3% increase over the 172,000 encountered in March, which had been the highest number in 20 years. 

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"CBP continues to see a large influx of illegal migration along the Southwest Border," acting CBP Commissioner Troy Miller said in a statement.

The agency said that the number of unaccompanied children from Northern Triangle countries dropped by 12%, with 13,962 in April compared with 15,918 in March. While single adults and some family units can be quickly expelled via Title 42 health protections, the Biden administration is not expelling unaccompanied children -- which has led to a dramatic spike in the number of children in custody and one that has overwhelmed border authorities.

However, while the Biden administration may be relieved it has not seen another spike of the one seen between February and March, the numbers are significantly higher than last year.

In April 2020, just 17,106 migrants were encountered. This means April 2021’s numbers are an approximately 940% increase over last year. It is also more than 60% higher than the numbers seen in April 2019, when the U.S. was also facing a significant border crisis -- 109,415 were encountered then.

Those April 2019 numbers, which were then exceeded the following month, were in turn followed by a sweeping number of moves by the Trump administration to curb migration. The Migrant Protection Protocols (MPP), which kept migrants in Mexico, were expanded, and asylum cooperative agreements were signed with Northern Triangle countries to allow migrants to claim asylum there instead.

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But the Biden administration has ended MPP and the Northern Triangle agreements, while also ending border wall construction and narrowing interior enforcement. Critics have said that those moves, along with not expelling unaccompanied children via Trump-era Title 42 health protections, have fueled the surge as migrants believe the border is open.

"The cause of the border crisis is entirely due to reckless federal policy reversals executed within your first 100 days in office," a letter from 20 Republican governors to Biden sent this week says. "The rhetoric of the Biden administration and the rollback of critical agreements with our allies have led to the inhumane treatment of tens of thousands of children and undermined a fragile immigration system."

The Biden administration has claimed that the border is not open, noting that most single adults and family units are expelled via Title 42.  In April, 111,714 migrants were expelled via Title 42, something that did not happen in 2019. It has also blamed the Trump administration for not being adequately prepared for the migrant surge.

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Separately, it has sought to emphasize the "root causes" of the crisis, pointing to violence, climate and poverty in Central America. The administration has proposed a $4 billion investment in the region, while Vice President Kamala Harris has called on countries like Japan and Finland to help out.

On Tuesday, Miller noted efforts by the Department of Homeland Security like Operation Sentinel -- a new project to crack down on transnational criminal organizations involved in smuggling migrants across the border.

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"In order to disrupt criminal organizations that have little regard for human life, CBP is leading the way alongside external law enforcement partners through Operational Sentinel. Day after day, CBP rescues migrants abandoned in harsh terrain, left for dead with no food or water. CBP is committed to enhancing the security of the U.S. border and helping save the lives of vulnerable migrants."

Harris is visiting Guatemala and Mexico at the beginning of next month, just days before the May border numbers will be announced.