Former acting Homeland Security Secretary Chad Wolf says Trump officials warned the incoming Biden administration that dismantling the Trump administration's immigration policies would cause problems at the southern border.

The Biden administration has largely blamed the challenges at the border on the previous administration, saying it gutted the Department of Homeland Security and used inhumane practices to try to deter migrants. Biden officials describe steps they've taken to accept the new influx of unaccompanied minors into the country and end controversial programs that require migrants to remain in Mexico as "a moral imperative."

But some former Trump administration leaders, such as Wolf, say the Biden administration is dismantling systems that worked.

"There is no consequence anymore," Wolf told NPR. "The administration is treating this as though it's a capacity issue and not an illegal behavior issue, and that's a fundamental difference."

Wolf was acting secretary from November 2019 until he abruptly resigned in January weeks before the inauguration following a court ruling that challenged the legality of his appointment.

He said he and his career staff held multiple briefings with the incoming Biden transition team to outline the challenges. He said they shared data that showed migration trends increasing since September and October 2020.

He said the Trump administration implemented programs such as "Remain in Mexico"; made asylum agreements with El Salvador, Guatemala and Honduras; and stopped allowing unaccompanied migrants to remain in the United States following the last migration crisis in 2019.

He said his staff at U.S. Customs and Border Protection warned the Biden team that it would risk another crisis if it removed those programs.

"CBP would tell them and, in a sense, warn them, 'If you remove this ... this is the consequence for that. We will see a significant uptick,' " he said.

But those programs were quite controversial and included reports of abuse and misuse. Asylum-seekers lived in squalid camps awaiting a court date. The New York Times reported that the Trump administration expelled some Central American migrants into Mexico.

Wolf said children were flown back to their home countries and received by government officials and taken home.

Homeland Security Secretary Alejandro Mayorkas acknowledged earlier this month that the administration was wrestling with the number of migrants — particularly unaccompanied minors — arriving at the border.

But he stressed there were more pressing moral imperatives to address in implementing immigration policy.

"Sometimes the tools of deterrence defy values and principles for which we all stand," Mayorkas said.

"And one of those tools of deterrence that the Trump administration employed was deplorable and absolutely unacceptable."

These surges in migration also appear to be cyclical. They occurred during the Obama administration in 2014 and again in 2019 during the Trump administration despite its harsh policies.

President Biden sent some of this top officials to Mexico and Guatemala this week to discuss how to address the root causes of migration.

Wolf agrees that the numbers would have likely increased as Biden took office regardless, but he argued that Biden's policies inflated the challenge. And he said that the U.S. government's resources wouldn't have been as taxed.

"We were telling them ... 'If you take down this, there's no capacity in Border Patrol stations. There's no capacity at HHS [facilities]. You will begin to have a backup. And here's the consequences to that.' "