Homeland Security Secretary Kirstjen Nielsen testifies on Capitol Hill in Washington on Wednesday before the House Homeland Security Committee. Credit: Susan Walsh | AP

Homeland Security Secretary Kirstjen Nielsen said the United States is on track to apprehend more than 900,000 migrants at the U.S.-Mexico border this fiscal year, as she pleaded with skeptical House Democrats on Wednesday to support President Donald Trump’s declaration of a national emergency to build a border wall.

After a major spike in border crossings last month, U.S. Customs and Border Protection is on track to detain far more than the 521,000 taken into custody in fiscal 2018, she said. That would require sustained border crossings at rates unseen in more than a decade.

Nielsen, testifying for the first time since Democrats took control of the House, said smugglers are encouraging families to file false asylum claims that virtually guarantee them entry into the United States, and she urged Democrats to support increased enforcement. She called the mass migration of Central American families arriving in cold, remote border outposts a “humanitarian catastrophe.”

“This is a legitimate national emergency,” she said before the Homeland Security Committee.

The hearing came a day after CBP Commissioner Kevin McAleenan said the migration system is “at a breaking point,” with soaring numbers of families surrendering in groups of 100 to 300 at a time.

CBP detained 76,103 migrants last month, the highest February since 2007, when almost 80,000 were apprehended. Of those who were detained last month, about 40,000 were parents and children traveling together, a 67 percent increase from January.

Democrats sought to downplay the rising numbers and criticized the administration for interfering with families seeking to legally apply for asylum. Homeland Security Committee Chairman Rep. Bennie Thompson, D-Mississippi, called Trump’s declaration “an emergency that does not exist.”

Rep. Jim Langevin, D-Rhode Island, pointed out that overall immigration flows are down significantly from 2000, when 1.6 million crossed illegally, and accused the president of “inflating” the magnitude of the situation.

Republicans prodded Democrats to set aside partisan politics to find a solution to the latest flows.

“We never argued about whether barriers worked until Donald Trump wanted them,” said ranking Republican Mike Rogers, of Alabama. “This is not rocket science.”

Nielsen told the committee that decades ago most border crossers were men. Now, the majority are parents traveling with children.

“It’s because these are families. It’s because these are children,” she said. “That is why it’s a crisis. It’s a terrible, horrific journey that they undertake.”

Other Democrats questioned Nielsen’s concern for the families when she engineered the forced separation of parents and children last spring. To deter illegal immigration, Nielsen and then Attorney General Jeff Sessions implemented a “zero tolerance” policy that sought to criminally prosecute all adults for crossing the border illegally, typically a misdemeanor, even if they were traveling with children.

Adults were detained and more than 2,700 children were separated from their parents and sent to shelters. The government did not have a tracking system in place, and a federal judge ordered officials to reunite them.

Last week, a federal official testified that he warned the Trump administration that separating parents and children could inflict long-term physical and psychological harm.

Rep. Nanette Barragán, D-California, told Nielsen that taking children from their parents was “outrageous.”